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Old October 19th, 2011, 06:12 AM   #41
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Quote:
Originally Posted by sotavento View Post
comuter trains usually go as high as 1,2 /2,5 m/s2

HSR trains usually have lower maximum acceleration usually as low as 0,5 /0,7 due to extremelly high gear ratios.
I wouldn't say 2.5 m/s^2, as that is sick fast. The upper limit is usually closer to 1.4 m/s^2 for conventional metro (subway) trains.
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Old October 19th, 2011, 04:32 PM   #42
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Quote:
Originally Posted by sotavento View Post
comuter trains usually go as high as 1,2 /2,5 m/s2

HSR trains usually have lower maximum acceleration usually as low as 0,5 /0,7 due to extremelly high gear ratios.
I'm unfamiliar with train transmissions, and considering the different scales of power involved, I assume they don't share any real similarities with automotive transmissions. Care to give a rudimentary explanation of how they work?

And also, those are all statements of how fast trains do go. How fast could they go before you started hearing passengers complain?
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Old October 19th, 2011, 11:45 PM   #43
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Quote:
Originally Posted by aquaticko View Post
I'm unfamiliar with train transmissions, and considering the different scales of power involved, I assume they don't share any real similarities with automotive transmissions. Care to give a rudimentary explanation of how they work?

And also, those are all statements of how fast trains do go. How fast could they go before you started hearing passengers complain?
You are right in saying they don't share fundamental similarities with automobiles, as auto transmissions are largely based off of planetary gear systems. The majority of "train transmissions" are the very simple and basic reduction gear design, where the motor drives a very small pinion that is geared to a large pinion that is connected to the actual axle of the train, as seen here (ignore that the motor is DC and just assume the general setup for any type of motor, AC or DC):



This yields for a single ratio transmission for trains as opposed to the multi-ratio transmissions found on On-Highway-Vehicles.

As for how fast trains can accelerate before passengers start to complain of G forces: I am aware of PCC street cars that have acceleration rates of up to 2.1 m/s^2. But the difference is that PCC's are single car consists that are light and small. To accelerate an HSR trainset that fast would require an enormous amount of power from the traction motors, which would arguably cause an uncomfortable amount of jerk in the initial start-up of acceleration as to render such an initial rate unfeasible.
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Old October 20th, 2011, 01:16 AM   #44
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Thanks for the information. I'm largely uneducated on the mechanics of trains, but I do know what a pantagraph is.

Much obliged, Fan Railer.
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Old October 20th, 2011, 11:14 AM   #45
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Quote:
How fast could they go before you started hearing passengers complain?
As fast as possible before the coffee spills onto the laps of passengers. But seriously, as Fan Railer states, the power levels required, and just operational necessity, keep things lower in general, than say, commuter rail stock.

A side note, and nitpick, but the DC motor drive w/pinion-gear setup is no longer used by most manufacturers for EMU designs, the standard is usually a cardan link connection between the traction motor (now usually AC on new stock) and the gear.
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Old October 22nd, 2011, 09:27 AM   #46
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Quote:
Originally Posted by sotavento View Post
comuter trains usually go as high as 1,2 /2,5 m/s2

HSR trains usually have lower maximum acceleration usually as low as 0,5 /0,7 due to extremelly high gear ratios.
I doubt about that. Commuter trains max accelereation is usually about 1,2m/s*s. But isn't it so that timetible is not maid on max acceleration? I have thought that timetable is maid using 50% acceleration maybe 70% acceleration. I think that into timetable is programmed some recovery time.
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Old October 22nd, 2011, 11:00 PM   #47
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Quote:
Originally Posted by ArtManDoo View Post
I doubt about that. Commuter trains max accelereation is usually about 1,2m/s*s. But isn't it so that timetible is not maid on max acceleration? I have thought that timetable is maid using 50% acceleration maybe 70% acceleration. I think that into timetable is programmed some recovery time.
Timetables are usually not based on constant acceleration, as trains do not have a constant acceleration.
The acceleration depends on the current speed, the higher the speed, the lower the acceleration. You can linearize this to get an information about the average acceleration between 0 and 100 km/h, but you can't base timetables on that:
If a train leaves from a station and the line allows a top-speed of 70 km/h, then the average acceleration based on 0-100 km/h is too low to get the correct time and distance which is necessary to reach 70 km/h.
And if the allowed speed changes from 70 to 100 km/h (due to different curbve radius eg) at a point where the train does not stop, then you must not calculate time/distance which is needed to accelerate from 70 to 100 km/h with the average acceleration between 0 and 100 km/h, because in reality the acceleration between 70 and 100 km/h is much lower.

That's why calculating exact travel times is a bit more complicated. You can do it by using 10 km/h-steps and the average acceleration for these 10 km/h steps.


Timetables are based on the lowest possible technical travel time for acceleration, constand speed and deceleration plus a certain percental buffer. The UIC recommends something between 6-9% (of the total time, not only the acceleration), but in reality this percentage should depend on the local situation.



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Old January 12th, 2012, 10:28 PM   #48
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Quote:
Originally Posted by PortoNuts View Post
Quote:
Originally Posted by trainrover View Post
Those Voyagers seem truly powerful (their acceleration, 0'20" )
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Old April 10th, 2017, 01:42 PM   #49
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I need some T-V curves (Tractive Effort - Velocity graph) for calculation of acceleration. Maybe somebody knows a web page/pdf/doc containing such a graph (should be referable). I need different suburban 0 - 160km/h and intercity 0 - 240km/h. Some modern stock would be preferable; for example such as siemens ES 64 or vectron. Both electric AC and diesel are needed. As long as the graphs can be read, they can be at any language. Thanks!
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Old April 10th, 2017, 02:37 PM   #50
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I haven't many clues but one is to follow a cabview on YouTube of a Thalys (TGV) between Rotterdam and Antwerp. Last time I found out one which also put the speedometer constantly in the screen, measuring the seconds and distances (use Google Earth or similar applications to carefully measure distance) are still up to you. On the Dutch rail then it takes 80 seconds to go to 140km/h over 1.5km with most EMU's (note however that this is only in the ideal situation and not in Rotterdam), thereafter is the part that the Thalys will really accelerate after some minutes watching.


Btw, in Dutch we call it a Tijd-wegdiagram, so if you Google it maybe something great rolls out.
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Old April 11th, 2017, 04:07 PM   #51
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Thanks for help. Ideally I would need something similar to this:

https://en.wikipedia.org/wiki/File:S...fort_curve.JPG
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Old April 11th, 2017, 09:10 PM   #52
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P=Fv
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Old April 12th, 2017, 01:48 PM   #53
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Quote:
Originally Posted by ArtManDoo View Post
I need some T-V curves (Tractive Effort - Velocity graph) for calculation of acceleration. Maybe somebody knows a web page/pdf/doc containing such a graph (should be referable). I need different suburban 0 - 160km/h and intercity 0 - 240km/h. Some modern stock would be preferable; for example such as siemens ES 64 or vectron. Both electric AC and diesel are needed. As long as the graphs can be read, they can be at any language. Thanks!
Quote:
Originally Posted by mrsmartman View Post
P=Fv
For modern trains using full variable drive technology the following method gives a good approximation:
  1. Look up the figures found on the internet
    e.g. ES64U2 (Taurus): 6400 kW, 300 kN, 230 km/h
  2. From 0 km/h up to the point maximum power is reached a train is tractive effort limited. Using mrsmartman's formula you can calculate that point:
    e.g. ES64: v=P/F=6400/300=21.33 m/s => 76,8 km/h
  3. Thus you can draw a straight line at 300 kN for speeds from 0 km/h to 76,8 km/h
  4. At speeds over this point tractive effort is power limited. Again using mrsmartman's formula you can calculate some points:
    e.g. F=P/v
    25 m/s (90 km/h) => F=6400/25=256kN
    30 m/s (108 km/h) => F=6400/30=213kN
    ...
    63,9 ms/ (230 km/h) => F=6400/63,9=100,2 kN
  5. Draw your data points in a graph
Using this method you will notice that the graph you end up with is very similar to the wikipedia example you reference. When you have additional figures you could compensate even further.

Using another formula (F=m*a) a solo Taurus locomotive could theoretically accelerate at 300/88=3,4 m/s^2 at low speeds (Yes, really, there are actual videos proving it), so you probably should limit acceleration to the values mentioned earlier for lower speeds.
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Last edited by M-NL; April 12th, 2017 at 05:30 PM. Reason: Fixed a typo (6400/90 isn't 256)
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Old April 12th, 2017, 02:12 PM   #54
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The formula was Newton's. Thanks for your explanation.
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Old April 21st, 2017, 03:27 AM   #55
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Revisiting the topic:

Quote:
Originally Posted by bluemeansgo View Post
Question: In general, is a multiple EMU setup ( like Shinkansen ) able to accelerate faster than a TGV, given similar tracks?

How do newer players (like Pendolino, Talgo and Zefiro ) fare when it comes to acceleration?
IT is all bassed in a "line-of-sight" aproach.

1- First of all we get the wheel diameter (the outer side of the wheel dish wich makes contact with the rails ... the bigger the wheels the faster the speed it can achieve (thus those old fast steam passenger locos had HUGE wheeels) ... nowadays usually HS Trains have 1,15m/1,3m diameter wheelsets (note to self: diameter = 2xRadius ... don't even ask)
2- then we get the gear ratios of the link transmission between the wheel axle and the traction motor ... the bigger the difference the faster it can go ... usual TGV transmissions have 2 sets of gearings and an intermediate articulated axle ... the motor is usually either suspended or FIXED onto to coach instead of the bogue/Axle for better unsprung weigth!
3- the power motor itself and what power/rpm it can generate
4- adding the "potential" speed achieved with this linkage we then must study how strong is actually the capacity of the motor to spin the transmission up to its great speeds.

Simple math:
A 1,15m wheel has a 3,61m circunference
At 300km/h a wheel travels 83m per second ... so we need some 23 rotations per second (1380rpm)

Complicated math: (some random variables to the equation... more exist)
- friction between rail-wheel wich is influenced by the axle weight of the train itself
- optimal power output at wich rpm settings
- ability of the trains to accelerate with 1(one) versus ALL axles powered
- power available in the motors themselves~

2 basic examples:
Loco+14 cars(+Loco?) = probably some 4x1500KW motors (conventional train with one or two locomotives or ICE/TGV push-pul set)
- has great tractive effort and power of acceleration in 4(8?) out of the 60(64?) total axles due to powerfull engines ...
- has potentially a great slippage problem at slower speeds due to preciselly its motors being that powerfull
EMU distributed power = various low power 300/500KW motors (like ICE3 and shinkansen)
- potentially low acceleration because the motors aren't powerfull enough (the lesser the number of powered axles worse is this problem)
- no problems with slippage and can achieve lower unsprung weight wich in itself lowers total power consumption at greater speeds (wich is the most inportant factor at greater speeds)

A full axles powered N700 trainset is the total oposite of a ton'n'tailed TGV Duplex because the TGV was meanth for long stretches in the countryside at full speed and the N700 was tailored for the comuter stop'n'go of the japanese tokkaido. The german ICE itself changed from the 1st(ICE1/2) to the 2nd(ICE3) in the same manner.

Newer models don't suffer from EITHER problem and thus are a mixture of both concepts with roughly 1/2 the axles powered by relatively small but powerfull traction motors (AGV ones have 1100KW already).


notice1: talgo high speed trainsets are conventional talgo sets top'n'tailed by TRAX bombardier locomotives with a duck nose. Nothing new in engeneering there (other than the old and tested talgo lightweight concept).
notice2: pendolino if not tilting in curves is a CONVENTIONAL train in itself with low power per axle and not even 1/2 axles powered.

Quote:
Originally Posted by Tri-ring View Post
I believe so since you have less load per powered axle providing more allowance for the wheels to apply torque to the rail without slippage. The down side is that it applies more weight and electro-magnetic resistance to the overall train set and motors requiring more overall power out to obtain faster top speed.
Power and braking power dictate acceleration and braking maximums ... the bigger and the more the merrier ... thus it's a balance between performance and cost in what equipment we put on the trains.
TGV have 4/8 high performance traction motors
N700 have 60(?) inexpensive traction motors

Quote:
Originally Posted by aquaticko View Post
I'm unfamiliar with train transmissions, and considering the different scales of power involved, I assume they don't share any real similarities with automotive transmissions. Care to give a rudimentary explanation of how they work?

And also, those are all statements of how fast trains do go. How fast could they go before you started hearing passengers complain?


TGV transmission:

Discussion on the subject here on SSC: (image came from there)
http://www.skyscrapercity.com/showth...age=2&langid=5


Quote:
Originally Posted by Fan Railer View Post
I wouldn't say 2.5 m/s^2, as that is sick fast. The upper limit is usually closer to 1.4 m/s^2 for conventional metro (subway) trains.
1.2m/s2 in regular operation could be tolerated in long distance trains
2.5m/s2 is the usual value considered acceptable for emergency braking ... wich in urban transit is put into effect in daily basis in many systems (especially in light rail/tramway usage) so I put it there.
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Old April 21st, 2017, 07:09 PM   #56
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The locomotive must be EXTREMELY powerful to haul a HSR train.
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Old April 23rd, 2017, 09:55 PM   #57
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Compared to what? Because in reality they aren't: The latest generation TGV power cars as used for the POS and 2N2 models 'only' have a 4640 kW power rating per car, whilst there are several current locomotive models with a 6400 kW power rating.

In fact realise that on a German Neubaustrecke with a 250 km/h limit an ICE2 would have a hard time beating a Railjet, given that most German cities aren't that far apart. A Railjet would accelerate much faster to it's 230 km/h top speed, helped by it's 6400 kW, whereas the ICE2's 4200 kW will need more distance to get to 250 km/h.
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Old April 24th, 2017, 06:22 PM   #58
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Locomotives designed for speed should be different from locomotives designed for tractive effort.
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Old April 24th, 2017, 10:40 PM   #59
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I guess you are looking at it from an American view, where not only the universal loco doesn't exist, but also electrics to pull freight trains are uncommon.

With the common in Europe 22,5t maximum axle load pretty much any modern electric loco can reach the maximum possible tractive effort of around 75 kN per axle, regardless of it's maximum speed. A German class 101 or a Taurus is just as happy pulling a passenger train at 200+ km/h as it is pulling a 'heavy' freight train at 80 km/h. A German class 145 can be used for passenger trains.

An ICE1/2 powercar is essentially a light weight German class 120 with a raised top speed and an aerodynamic body shell. The only real difference is that locos with a lower top speed use less sophisticated cheaper bogies. Except for the IORE maybe, I don't know of any European electric loco that can't provide HEP.

It didn't use to be this way though. A German class 103, for instance, is totally unsuitable for pulling a freight train.
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Old April 24th, 2017, 11:40 PM   #60
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Quote:
Originally Posted by nachalnik View Post
Timetables are usually not based on constant acceleration,


Best regards


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Incidental question: are you the OEBB guy who used to have a blog on rail travel to far away Asian destinations?
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