Idea for additional non-friction Train braking

[matacaster]

A particular problem that affects trains and track capacity is the speed with which trains can stop. The ability to stop questions quickly is governed by the maximum rail adhesion before wheelslip occurs and basically the train skids. More wheels and greater weight help, but the reality is stopping takes far longer than a rubber tyre / road combination.

Additional non-friction braking could be supplied by say an electrically driven turbine which only worked at high speeds to dramatically reduce the time taken to stop and hence lead to better track utilisation. Provision of such a turbine would be costly, but how about it? may be cheaper than new infrastructure?

 

[TRAX]

The issue here is the weight and momentum of trains.
Regenerative braking is already pretty efficient to stop trains, and effectively enables the friction brakes to almost only be used at the very end of the braking sequence, near standstill. I can’t think of many systems, turbines or else, that would be an efficient addition to the already efficient regenerative braking systems.
Also, the whole point of regenerative braking is being able to feed electrical current from braking back to the network (a modern EMU can send 20 % of its electricity consumption back to the network), permitting good energy savings to be made. If you start using electrical energy during braking (which seems a bit counter-intuitive) to feed your ‘braking turbine’ instead of sending it back, how big a backstep would that be ?

 

[pdeaves]

In addition, consider comfort/safety for those on board. Heavier braking than we have now, at just the point that people start moving towards doors to alight, is asking for trouble. Doesn't apply to freight, of course, but we still don't want drivers head butting their controls!

 

[Chuggington21]

A particular problem that affects trains and track capacity is the speed with which trains can stop. The ability to stop questions quickly is governed by the maximum rail adhesion before wheelslip occurs and basically the train skids. More wheels and greater weight help, but the reality is stopping takes far longer than a rubber tyre / road combination.

Additional non-friction braking could be supplied by say an electrically driven turbine which only worked at high speeds to dramatically reduce the time taken to stop and hence lead to better track utilisation. Provision of such a turbine would be costly, but how about it? may be cheaper than new infrastructure?

I may have understood you incorrectly however most modern day trains are electrically braked and friction brake is only used below a certain speed or to supplement the electrical (dynamic/rheostatic) brake

 

[hexagon789]

A particular problem that affects trains and track capacity is the speed with which trains can stop. The ability to stop questions quickly is governed by the maximum rail adhesion before wheelslip occurs and basically the train skids. More wheels and greater weight help, but the reality is stopping takes far longer than a rubber tyre / road combination.

Additional non-friction braking could be supplied by say an electrically driven turbine which only worked at high speeds to dramatically reduce the time taken to stop and hence lead to better track utilisation. Provision of such a turbine would be costly, but how about it? may be cheaper than new infrastructure?

What does the turbine do to slow the train?

 

[hexagon789]

I may have understood you incorrectly however most modern day trains are electrically braked and friction brake is only used below a certain speed or to supplement the electrical (dynamic/rheostatic) brake

The brakes are electrically controlled on most trains but friction brakes (disc or tread) are the only brake on many DMUs and EMUs in service.

 

[matacaster]

Even electrically controlled braking works through the contact between wheel and rail, so slipping can surely occur if the braking is too quickly applied?

 

[hexagon789]

Even electrically controlled braking works through the contact between wheel and rail, so slipping can surely occur if the braking is too quickly applied?

I assume you mean rheostatic/renerative braking rather than actual electrically-controlled/actuated braking?

Yes, typically if the WSP detects slipping on a rheostatic/regenerative-braked train it will inhibit these forms of braking and refer to to pure friction braking.

The only forms of braking I'm aware of that aren't not restricted by avaliable wheel-rail adhesion are electromagnetic or eddy-current braking. The former is often used on trams/light rail, some Continental European coaching stock/units; the latter is on some German ICE trains and possibly other high-speed trains.

 

[Intellectual98]

Are you essentially suggesting a big fan at the front of the train blowing air forwards? That will do somewhere in the region of diddly squat to stop a train. A jet engine might to something helpful but have you considered the fact that high speed jets of air aren't going to be good for passengers on platforms.

Much more useful in low adhesion situations would be an additional friction brake that is magnetically attracted into to the railhead. This is something that is already in use on some street level trams where emergency brakes have to meet more stringent deceleration requirements. It would have the added benefit of scrubbing the contamination from the railhead but with the disadvantage of increased railhead wear.

 

[hexagon789]

Much more useful in low adhesion situations would be an additional friction brake that is magnetically attracted into to the railhead. This is something that is already in use on some street level trams where emergency brakes have to meet more stringent deceleration requirements. It would have the added benefit of scrubbing the contamination from the railhead but with the disadvantage of increased railhead wear.

Electro-Magnetic track brakes. I believe DB fitted them to coaches way back in the 1960s to allow 200km/h. (Otherwise it was 160 max on discs or 140 on treads.) Only used in emergency though, not for service braking afaiaa.

 

[Intellectual98]

Electro-Magnetic track brakes. I believe DB fitted them to coaches way back in the 1960s to allow 200km/h. (Otherwise it was 160 max on discs or 140 on treads.) Only used in emergency though, not for service braking afaiaa.

Exactly these, just didn't know the name. Never seen them in the UK, but I know they exist.

 

[hexagon789]

Exactly these, just didn't know the name. Never seen them in the UK, but I know they exist.

Many trams have had them; not sure if they've ever been used on heavy rail in the UK.

 

[TRAX]

Many trams have had them; not sure if they've ever been used on heavy rail in the UK.

You have them on the Nottingham Citadis trams as all Citadis have them. Not sure if anything else in the UK has some. None on any heavy trains, that’s for sure.

 

[hexagon789]

You have them on the Nottingham Citadis trams as all Citadis have them. Not sure if anything else in the UK has some. None on any heavy trains, that’s for sure.

I know that they had them on some Glasgow trams and that's going back a bit! Whenever they are used it always seems to be for emergencies though, probably because they can damage track when used I believe.

 

[Bletchleyite]

On DB stock they aren't tram-style track brakes (they don't clamp to the track), they are eddy current brakes which work by inducing eddy currents in the railhead by way of an electromagnet.

 

[hexagon789]

On DB stock they aren't tram-style track brakes (they don't clamp to the track), they are eddy current brakes which work by inducing eddy currents in the railhead by way of an electromagnet.

Not on ICE trains which are Eddy current brakes as you say (I know the ICE3 has them not sure about ICE1/2), but on older coaches they are/were EM track brakes.

 

[TRAX]

I know that they had them on some Glasgow trams and that's going back a bit! Whenever they are used it always seems to be for emergencies though, probably because they can damage track when used I believe.

On the Citadis trams (and regional trains in France for all I know) the track brakes lower smartly when the emergency brakes are applied. And yes indeed they do damage the track quite badly when used.

 

[hexagon789]

On the Citadis trams (and regional trains in France for all I know) the track brakes lower smartly when the emergency brakes are applied. And yes indeed they do damage the track quite badly when used.

Probably a combination of the increased friction and the way they pull the vehicle down onto the track.

 

[TRAX]

Yes, it really grabs the rail like there’s no tomorrow, and does so very fast with a loud bang.

 

[Indigo Soup]

I believe that some of the higher-performance Shinkansen have air brakes - literally just whacking great bits of metal that can be opened to increase the drag of the train. No idea if these are intended for emergency use or normal service braking.

 

[edwin_m]

Disc brakes on steel wheels can get in the region of 10%g deceleration, limited as mentioned by the coefficient of friction to the rail. Regeneration could do the same if all axles were motored, but they usually aren't. To save energy it may be appropriate to plan the timetable based on using regeneration only, but to plan the minimum headways based on maximum available braking. That way the friction brakes only get used when something unexpected happens.

Track brakes are effectively extra because they create extra reaction force between the train and the track that doesn't depend on the weight of the train. They do depend on the coefficient of friction but the scrubbing action of a track brake may be better at removing rail contamination than the rolling action of a wheel. Having said that there's at least one tram collision on the RAIB website attributed to rail contamination.

Also, the maximum comfortable acceleration and deceleration for passengers who may be standing is also around 10%g, especially if the rate of deceleration may change suddenly, as it tends to when track brakes apply. The rubber-tyre Metro routes in Paris achieve a bit more, but they have notices inside warning people of the hard braking so I suspect there have been some injuries. All modern trams I'm aware of have track brakes, but it's kept in reserve for unexpected events such as a pedestrian or other vehicle suddenly crossing its path, and may be referred to as a hazard brake. Tram drivers are trained to drive at a speed from which they can stop comfortably short of any obstruction ahead using only the service brake.

 

[hexagon789]

I believe that some of the higher-performance Shinkansen have air brakes - literally just whacking great bits of metal that can be opened to increase the drag of the train. No idea if these are intended for emergency use or normal service braking.

Emergency I believe, I seem to recall reading it was the only way they could stop from top speed in the specified distance in emergency.

 

[Ken H]

On DB stock they aren't tram-style track brakes (they don't clamp to the track), they are eddy current brakes which work by inducing eddy currents in the railhead by way of an electromagnet.

Isnt an objection to that that that heats the rail head, and that may change the properties of the steel over time?

 

[Ken H]

with ac motors, whose speed is set by the frequency of the supply (The electronics varies the frequency to accelerate the train) when regen braking, dont they keep the wheels turning at the current speed of the train minus a little, thus giving the braking. But as the wheels keep turning you dont get wheel-slip.

But keeping the rail head clean would be the best - but that seems difficult. Anyone remember the Swedish Scrubber?

 

[Bald Rick]

Both friction and regeneration braking could stop trains at a much higher rate than the 9%g service 12%g emergency rates in use on GB national rail. They are not designed to simply because of passenger comfort. Other railways have different principles, not lest the Underground and DLR.

 

[ijmad]

How about arrester hooks and a steam catapult at every station.

Similar to an aircraft carrier.

 

[GreatAuk]

... To save energy it may be appropriate to plan the timetable based on using regeneration only, but to plan the minimum headways based on maximum available braking. That way the friction brakes only get used when something unexpected happens.

... Track brakes are effectively extra... .

I have wondered in the past whether an approach like this could help increase capacity. Especially with potential future moving block systems - you could timetable the trains so that normally they would only use regen, but in an emergency they could pull up very quickly, reducing the required separation.

Could use any system to achieve the extra braking, as long as its reliable - be it track brakes, eddy current brakes, or something else. Only using the system in emergencies would also negate worries around long term damage to track etc.

As mentioned above I believe the Shinkansen trains use this sort of philosophy to allow them to run very fast while still being able to stop quickly in event of an emergency (including an earthquake!)

 

[edwin_m]

I have wondered in the past whether an approach like this could help increase capacity. Especially with potential future moving block systems - you could timetable the trains so that normally they would only use regen, but in an emergency they could pull up very quickly, reducing the required separation.

Could use any system to achieve the extra braking, as long as its reliable - be it track brakes, eddy current brakes, or something else. Only using the system in emergencies would also negate worries around long term damage to track etc.

As mentioned above I believe the Shinkansen trains use this sort of philosophy to allow them to run very fast while still being able to stop quickly in event of an emergency (including an earthquake!)

Yes, HS2 plans to use this approach. The friction brakes will still be fully certified to stop the train an unlimited number of times but are intended only to be used if the train in front needs to slow down unexpectedly. That's not quite the same thing as emergency-only brakes, which may require maintenance attention after a limited number of applications.

 

[randyrippley]

there's a simple solution to all this..........combine magnetic braking with a Fell rail system
if you don't know what the Fell system is, see
https://en.wikipedia.org/wiki/Fell_mountain_railway_system

 

[LOL The Irony]

there's a simple solution to all this..........combine magnetic braking with a Fell rail system
if you don't know what the Fell system is, see
https://en.wikipedia.org/wiki/Fell_mountain_railway_system

That'll be possible on standard track but not really HS2. The bottom of the trains have to be as smooth as possible.