Would a Brake-by-wire system improve braking performance?

[GLC]

While reading some of the discussion of the Salisbury collision, I saw a post describing how early WSP algorithms were limited in their effectiveness, as the application rate of the brakes had to be limited so as not to exhaust the air supply of the train.

This got me thinking, if there is any reason that trains are not equipped with electrically actuated brake pads, supported by a brake by wire system? I understand the two pipe brake system used in trains today has a safety record proven over decades, which obviously should not be thrown away lightly. But if there is a constraint on brake applications in emergency situations, is there really no practical alternative system today, or is there anything in development?

 

[Bletchleyite]

Isn't this exactly the sort of thing that the "Westcode" brake system used on Class 15x is? Though actual application is still by air.

 

[hexagon789]

While reading some of the discussion of the Salisbury collision, I saw a post describing how early WSP algorithms were limited in their effectiveness, as the application rate of the brakes had to be limited so as not to exhaust the air supply of the train.

This got me thinking, if there is any reason that trains are not equipped with electrically actuated brake pads, supported by a brake by wire system? I understand the two pipe brake system used in trains today has a safety record proven over decades, which obviously should not be thrown away lightly. But if there is a constraint on brake applications in emergency situations, is there really no practical alternative system today, or is there anything in development?

I understood the system used on 158/159 and indeed on most MU trains built after about 1975-1980 was essentially an electric "brake-by-wire" system. On 15x it's called Westcode and uses electric signals to control the brakes. The brakes are held off by the system, so if it fails they come on. Air still effects the physical application of pads/shoes onto the wheels but control is electric rather than pneumatic.

There is also a governor fitted to ensure that the brakes are dumped to emergency long before there isn't any air to do so.

 

[edwin_m]

Braking systems that are electrically controlled but use air pressure to provide the brake force are universal on modern MUs and similar systems are used on some wagons in North America. But as far as I'm aware nobody uses electric actuators to provide the actual brake force, which is I presume what the OP is suggesting to get round the problem of using too much air when WSP is active.

 

[Irascible]

Braking systems that are electrically controlled but use air pressure to provide the brake force are universal on modern MUs and similar systems are used on some wagons in North America. But as far as I'm aware nobody uses electric actuators to provide the actual brake force, which is I presume what the OP is suggesting to get round the problem of using too much air when WSP is active.

The other thing it'd get round would be application/release time, which would be more or less instant. I'm not sure *any* transport has direct application via electromagnets though ( unless you ciount emergency rail shoes ), if it's not pneumatic it's hydraulic. It'd be a lot easier to do most of the WSP in regenerative braking for new stuff ( given it's more or less all electric transmission ).

There is a debate also as to whether you can fail-safe a pneumatic system & reservoir better or worse than an electrical system + battery.

 

[Bletchleyite]

The other thing it'd get round would be application/release time, which would be more or less instant.

Again, Westcode on 15x is for this purpose. HSTs also have electronically controlled additional actuation from both ends.

I'm not quite sure why more recent DMUs and EMUs have reverted to the classic air brake.

 

[Irascible]

Again, Westcode on 15x is for this purpose. HSTs also have electronically controlled additional actuation from both ends.

I'm not quite sure why more recent DMUs and EMUs have reverted to the classic air brake.

Not quite what I was getting at, Westcode still uses venting air in & out of brake cylinders - the speed at which actuation is detected ( ie transmitted via wire or pipe ) doesn't change that, and also either 3 or 4 wires - someone remind me before I have to root around for a manual! - which are either energised or not, so not amazing for fine control. That bit doesn't matter for normal use, but for really effective antislip you're looking at multiple cycles per second with some precision control of pressure - somewhat academic because I doubt any rail vehilcle is specced with that level of control, but I think that's what the OP was imagining. Electromagnetic brakes - disk or shoes - would be instant. Also comparatively heavy, I'd imagine. Holding the brakes at the rough pressure you want & using traction motors to fine tune the retardation sounds rather more practical, although obviously not much use on a Sprinter.

There were some other issues with Sprinter WSP I think, but it's been over a decade since I had to poke my nose into that so I've forgotten any details.

 

[edwin_m]

The other thing it'd get round would be application/release time, which would be more or less instant. I'm not sure *any* transport has direct application via electromagnets though ( unless you ciount emergency rail shoes ), if it's not pneumatic it's hydraulic. It'd be a lot easier to do most of the WSP in regenerative braking for new stuff ( given it's more or less all electric transmission ).

There is a debate also as to whether you can fail-safe a pneumatic system & reservoir better or worse than an electrical system + battery.

Yes, if you're wanting to do something like this, you'd probably just motorise all the wheels and use regenerative braking, giving better acceleration too. However a pneumatic system would be much easier to prove to be failsafe, being relatively simple with predictable failure modes and getting on for 150 years of service experience.

BR Research produced an experimental all-electric vehicle in about 1990, re-using one car of the Class 210 prototypes. It must have had some sort of electric brake too, but I either never knew the details or have forgotten. Web search doesn't show anything up, there may be a report somewhere in the RSSB/SPARK database as a lot of the research reports went there, but it's not letting me log in at the moment.

 

[HSTEd]

Yes, if you're wanting to do something like this, you'd probably just motorise all the wheels and use regenerative braking, giving better acceleration too. However a pneumatic system would be much easier to prove to be failsafe, being relatively simple with predictable failure modes and getting on for 150 years of service experience.

BR Research produced an experimental all-electric vehicle in about 1990, re-using one car of the Class 210 prototypes. It must have had some sort of electric brake too, but I either never knew the details or have forgotten. Web search doesn't show anything up, there may be a report somewhere in the RSSB/SPARK database as a lot of the research reports went there, but it's not letting me log in at the moment.

There is a lot of work in America associated with EPS brakes where they are talking about automating the application and release of handbrakes by fitting clutched motors to the handbrake wheels - so the handbrakes can be put on and off at once at the push of a button from the cab.

== Doublepost prevention - post automatically merged: 26 Feb 2022 ==

Not quite what I was getting at, Westcode still uses venting air in & out of brake cylinders - the speed at which actuation is detected ( ie transmitted via wire or pipe ) doesn't change that, and also either 3 or 4 wires - someone remind me before I have to root around for a manual! - which are either energised or not, so not amazing for fine control. That bit doesn't matter for normal use, but for really effective antislip you're looking at multiple cycles per second with some precision control of pressure - somewhat academic because I doubt any rail vehilcle is specced with that level of control, but I think that's what the OP was imagining. Electromagnetic brakes - disk or shoes - would be instant. Also comparatively heavy, I'd imagine. Holding the brakes at the rough pressure you want & using traction motors to fine tune the retardation sounds rather more practical, although obviously not much use on a Sprinter.

Well a more modern electronically controlled solution can generate that level of control - also why wouldn't the antislip just be done on the vehicle once you have an electronics box on it to decode the brake signals anyway?

And I'm not sure we should really consider applying the brakes then trying to power through them a particularly elegant solution to the fine control problem!

 

[Irascible]

And I'm not sure we should really consider applying the brakes then trying to power through them a particularly elegant solution to the fine control problem!

I don't know why you would do that, or even think of doing that.

 

[HSTEd]

I don't know why you would do that, or even think of doing that.

Well it is common practice in North America, where it is referred to as "Power Braking".

How else do you propose to use traction motors to fine tune retardation?

 

[GC class B1]

Well it is common practice in North America, where it is referred to as "Power Braking".

How else do you propose to use traction motors to fine tune retardation?

This used to occur on the Westinghouse air braked (pre- electro pneumatic braked) SR emus which had a triple valve. With this system which was in common use in the USA the air brake was graduated application but not graduated release unlike the UIC brake where the brake can be partially released by increasing the Brake pipe pressure. The brake would release completely when the brake pipe was recharged to a value above the application pressure. If the driver was going to stop too early he would apply traction as releasing the brake could result in an overrun, especially a problem at terminal stations.

 

[Irascible]

Well it is common practice in North America, where it is referred to as "Power Braking".

How else do you propose to use traction motors to fine tune retardation?

That is probably because they don't have graduated release, it's all or nothing ( triple valve operation described above now I read it properly ) - rather like pinning brakes down & then dragging wagons, like we used to do. IIRC US passenger stock does have distributors ( now, anyway ) & can vary release.

We have fine enough control over motors to be able to friction brake to not quite the slipping point & then use the motor for the rest of it. Whether you use the motor as a generator ( regen/rheo ) or apply some power to it & run it in a retardation mode if you're really slow & can't apply enough forice in a regen mode, whatever. I can see how you could manage it with a squirrel-cage motor but have to say I don't know anything about how modern AC permanent-magnet motors work. Either way it'd provide faster response than moving air around would. Admittedly only on powered axles...

I still debating the actual need for something that responsive, though I guess if you can do it in software ( er, right ) then why not - variably blending regen & friction braking is not a new concept but that fine level of control, I don't know.