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Brake is stronger than emergency brake

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Brake is stronger than emergency brake Empty Brake is stronger than emergency brake

Post by LXQt Fri Mar 27, 2020 1:05 pm

So I am making an light rail train, it has 5 power notch and 5 brake notch(B5-P5)
What I am noticing is if I use the emergency brake, it will decelerate very slowly(maybe not even B1 or B2), I've looked up the documentation yet it doesn't seems that you can set the deceleration rate of an emergency brake, could anyone tell me which part affects the emergency brake decel rate? Thanks.

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Brake is stronger than emergency brake Empty Re: Brake is stronger than emergency brake

Post by leezer3 Fri Mar 27, 2020 7:26 pm

EB ought to be stronger than the final brake notch.
IIRC it should be about +20% on it as a rough rule of thumb.

Depending on the brake setup, it may also be affected by the acceleration settings. The delay value may also be coming into play.

Any chance of the train.dat so I can see what's going on? (Don't need any of the motor sections or anything)
That's the easiest way to see if it's the sim or something in the setup.

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Post by LXQt Sat Mar 28, 2020 2:03 am

Here we go https://drive.google.com/open?id=1Z5EHkdspGw4Py_dV3kxHI_5UUJZGkks9

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Brake is stronger than emergency brake Empty Re: Brake is stronger than emergency brake

Post by Ghost of Kymlinge Sat Mar 28, 2020 4:46 pm

In real life, a full-service braking may produce a better stopping distance than emergency braking. A test conducted by the NTSB, following an accident in the New York subway, showed such result:

A subway train consisting of eight R40 cars travelling at 34 mph had a stopping distance at a certain wet track of 162’10” using full-service braking. Applying the emergency brakes at the same wet track and speed caused a stopping distance of no less than 358½’. The result was, as I understand it, attributed to wheel lockup and slipping using the emergency brakes in wet conditions

Tests conducted on dry track however showed the opposite and more expected result that emergency braking made the stopping distance shorter than full-service braking.


[Source: NTSB report NTSB/RAR-96/03, page 20, 35]
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Brake is stronger than emergency brake Empty Re: Brake is stronger than emergency brake

Post by LXQt Sat Mar 28, 2020 5:00 pm

Ghost of Kymlinge wrote:In real life, a full-service braking may produce a better stopping distance than emergency braking. A test conducted by the NTSB, following an accident in the New York subway, showed such result:

A subway train consisting of eight R40 cars travelling at 34 mph had a stopping distance at a certain wet track of 162’10” using full-service braking. Applying the emergency brakes at the same wet track and speed caused a stopping distance of no less than 358½’. The result was, as I understand it, attributed to wheel lockup and slipping using the emergency brakes in wet conditions

Tests conducted on dry track however showed the opposite and more expected result that emergency braking made the stopping distance shorter than full-service braking.


[Source: NTSB report NTSB/RAR-96/03, page 20, 35]
This wasn't the case, if I use emergency brake, it is barely braking(took 3 second to decelerate 1km/h, not really my expectation)

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Brake is stronger than emergency brake Empty Re: Brake is stronger than emergency brake

Post by Drag0nflamez Sat Mar 28, 2020 8:11 pm

Ghost of Kymlinge wrote:In real life, a full-service braking may produce a better stopping distance than emergency braking.
Not to mention possible differences between electric braking and friction brakes.

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Post by jorgecerezo Sun Mar 29, 2020 6:23 pm

Looking at your train.dat, I see a problem with the Pressure section. You are using very high unrealistic values in my opinion. In order to make them work properly, you need to use this Brake section:

#BRAKE
1              ; BrakeType
0              ; BrakeControlSystem
0              ; BrakeControlSpeed

Alternatively, if you want to continue using the Electromagnetic straight air brake, BrakeType=0, you need to use this Pressure section:

#PRESSURE
1800           ; BrakeCylinderServiceMaximumPressure
3000           ; BrakeCylinderEmergencyMaximumPressure
3000           ; MainReservoirMinimumPressure
3500           ; MainReservoirMaximumPressure
3000           ; BrakePipeNormalPressure

According to my calculation these pressure values should give you a emergency deceleration rate of 5.17 km/h/s

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Post by leezer3 Sun Mar 29, 2020 6:42 pm

I agree, your #PRESSURE section is broken.
Remember that the figures here are in kPa.

Some thoughts:
* The BrakePipeNormal pressure should be nominally somewhere near double the service max pressure, and at approximately the EB pressure. Higher than this is fine.
* I think you've got Pascals and Kilopascals confused in everything except the BrakePipeNormal pressure. 
* The default compressor setup recharges 5kPa of pressure per second. Assuming you make an EB application from running conditions with the main reservoir full, you'll take 10 minutes to recharge the main reservoir fully, which is completely broken.
* Similarly, most of the brake pipe etc. flow rates are in the range of 5kPa /s (normal) and 25kPa /s (EB), so your current setup will not be happy at all.

(I haven't played with this directly in-game as the figures make no sense. If it's otherwise 'working' I'd guess Michelle's code to be doing the best it can)

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Post by leezer3 Sun Mar 29, 2020 7:20 pm

I've now added the default flow rates to the train.dat documentation.

(This is primarily as a FWIW, but they might provide some insight into the workings of the brake system)

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Post by Northern Line Wed Apr 01, 2020 3:48 am

Drag0nflamez wrote:
Ghost of Kymlinge wrote:In real life, a full-service braking may produce a better stopping distance than emergency braking.
Not to mention possible differences between electric braking and friction brakes.

I'm sure if you apply EMG brakes it's full friction brakes, the electric brakes would cut out? I could be wrong  Neutral
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Post by Quork Wed Apr 01, 2020 3:36 pm

Argh, damn Windows 10 and its stupid "gestures". I casually flicked off some dust particle from the touchpad and accidentally triggered some "go back a page" gesture - now the detailed text I've been working nearly an hour on is gone. I hate it!

Maybe I'll have the nerve to write it again some other time, not now. So here's the short answers:
- no, electric brakes don't cut out at EB, usually. There might be some exots, and in other "railway traditions/cultures" there might be other philosophies, but in continental Europe at least dynamic (electric, hydrodynamic, whatever) brakes are prioritised, because their force is available the fastest and they can be regulated way more finely, meaning you can go much closer to the frontiers of what's possible frictionwise. There are some limitations to that as in some locomotives giving less electric brake force at EB than at service brakes; but that's because they aren't designed for solo driving but by taking the whole train into account. You don't want to over-brake the train because funny things would happen with slip protection, resulting in worse braking. So a solo locomotive in some instances might actually brake worse at EB than at full service brakes, being the only exception to the next bullet point. That's also one of the reasons why you mustn't take engine brakes into account for brake calculation unless there's at least four independently air braked vehicles in the train, meaning a solo locomotive's speed limits are calculated as if it had air brakes only.
- EB is always at least as strong as full service brake setting. Period.
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Post by zbx1425 Thu Apr 02, 2020 2:18 am

Well, I thought electro-magnetic brake cut-out on emergency application is common! As far as I have known, at least it applies to most Japansese and Chinese EMUs and locomotives. Some of the trains would even lower the pantograph automatically once emergency brake is applied. 

And since BVE is a Japanese simulation game, I'm afraid it would do that too. Haven't searched through the source code yet, so I am not quite sure. But I remembered that motor noise is not played when emergency brake is applied.
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Post by Quork Thu Apr 02, 2020 3:41 am

Now that you mention it, I seem to remember a video from a Japanese EMU showing the brake cylinder pressure raising at the change from service brake to EB. That would mean a different approach, making the braking more independent from OHL voltage at the cost of being more vulnerable to wheel slip. But it still would mean an at least equal brake force (that is, if no slip occurs).

A small addition: What happens when OHL voltage drops off, an engine or other electrical fault occurs or engine brake force drops off/out because of other reasons?
The brake valve always produces a brake cylinder pressure, it is only cut off by an electromagnetic valve. When the electric brake force drops off partially/completely, the "prepared" brake cylinder pressure is released to the brake cylinders accordingly (partially/completely). Depending on the vehicle and the situation (anticipated partial drop-offs (e.g. because of low speed) vs. sudden, unexpected changes (e.g. voltage gone)) this process can be anything between very smooth and taking a substantial fraction of a second (resulting in a "jump" forward).
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Post by zbx1425 Thu Apr 02, 2020 4:33 am

I think the brake controllers on a lot of EMUs are quite clever, that they calculate a desired deceleration based on the driver input, and order the inverter to apply a certain amount of dynamic brake. If it finds out that the deceleration produced by the inverter is not enough, then it would deploy a small amount of air brake to fill it up.
For example, on the DKZ9 series rolling stock at my city, the IGBT inverter is not very efficent at dynamic braking, and when the train pulls in you can hear the brake shoe rubbing sound along with the motor noise, indicating the brake controller is having them working simultaneously to fullfill the brake deceleration commanded by the driver. And the dynamic brake is cut off at around 10 kph so a sudden boost in the volume of the rubbing sound can be heard.

I actually cannot understand the "dynamic brake cuts out when emergency brake commanded" logic. There must be a reason behind this but I didn't know so far. Maybe they are afraid the current caused by strong braking might damage the inverter? Or maybe just in case the inverter fails and is powering the motors regardless of the driver's input, then it provides a way to cut them off easier?
But there are accidents caused by this. I remember once on China Railway, the air brake failed on a passenger train, and the driver not knowing that tried to apply emergency brake but appearantly that would not help. To make things worse, the emergency brake application cuts out the dynamic brake, and it could not be reenabled! (What a silly design) Fortunately there was a safer siding available at the next station so no head-on collision, but major injuries still resulted.
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Post by Quork Thu Apr 02, 2020 10:37 am

Yeah, modern vehicles do more and more of this stuff via computer calculation, but the general way it works is still the same.

There is no real risk of the inverter frying itself - with asynchronous three-phase motors the inverter has to induce the engine to be able to use it as a generator, so the current is limited by what the inverter is able to induce in the first place. But that's also why dynamic braking is dependent on external voltage. If that's gone, the brake force is gone.

So once possible reason for having a design without electric braking in EB would be to ungo the possibility of temporary partial brake power loss in the event of electrical failure etc. and to not have to cope with needing to blend pneumatic brakes in once the electric brakes fade out due to low speed.

I don't know the vehicle you've mentioned, so I can't be sure, but my guess is the dynamic brakes aren't cut off but simply fade out. Especially with older inverters the force collapses at quite high speeds already, especially with GTO or even classical thyristors. Modern IGBT inverters usually can generate high braking forces even at very low speeds. Even a class 101, which is a quarter of a century old already, has noteworthy electric brake force down to about 2 or 3 km/h and still noticeable brake force at barely above standstill.

The inverter is powered in a different way for braking than for acceleration. Well, theoretically you could do it the same way and brake by "accelerating backwards" so to say, but that would mean *using* power for braking. I'm not aware of any design doing this. You want to use the engine as a generator for braking; either to recuperate the energy or at least to "burn it off" on resistors, which is still better than using even more power for braking.
But because of that there's not really a risk of accidentally accelerating instead of braking.
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Post by zbx1425 Thu Apr 02, 2020 11:07 am

Quork wrote:I don't know the vehicle you've mentioned, so I can't be sure, but my guess is the dynamic brakes aren't cut off but simply fade out. Especially with older inverters the force collapses at quite high speeds already, especially with GTO or even classical thyristors. Modern IGBT inverters usually can generate high braking forces even at very low speeds. Even a class 101, which is a quarter of a century old already, has noteworthy electric brake force down to about 2 or 3 km/h and still noticeable brake force at barely above standstill.
Well, it seems that the regenerative brake and air brake are always working simultaneously, at least according to what I've heard.
The rubbing sound and the motor noise went simultaneously even at around 40kph. But not that much rubbing sound at 60kph or 80kph, so I guess the brake controller is not well-tuned to work with the IGBT, so it is not commanding the IGBT to give out enough braking power at lower speeds, and has to use air brake to fill it up. The rubbing sound gets appearantly louder as the speed gets lower.
It is appearant that IGBT is cut out at around 10kph almost instantly. The really loud motor sound just stops all of a sudden.

Another batch of the same model got produced in 2018, and the new trains have different IGBT and brake controller than the old trains. The difference is quite appearant. The IGBT on the new trains does all the braking until the train comes to a stop, and no rubbing sound can be heard. The air brake only kicks in after the train become still. I have not encountered an emergency brake application on the new trains, so I don't know how its braking work. But the electro-magnetic brake does cut out at emergency brake application and at low speed on the old trains.
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Post by jorgecerezo Thu Apr 02, 2020 7:08 pm

I understand EMUs with electro-magnetic brakes cut out dynamic brakes in emergency braking to prevent wheels locking up. A typical 1.2 m/s2 decceleration requieres 0.12 adhesion coefficient, which is lower than 0.15, typical value representing adverse conditions. The combination of both types of braking exceeds the safe 0.15 value, that is the reason why they are not used together in emergency.

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Post by Quork Thu Apr 02, 2020 10:12 pm

And that appears to be the difference in different "cultures" of railway. Here usually it's the air brake that is cut out, because electric brakes can adjust better/faster to adverse conditions. However I've remembered a big exception to almost anything about brakes in Central Europe: Class 423/425/426. That family of trains was the first (and until very shortly ago only) here to have direct electropneumatic brakes: In normal operation it doesn't use its brake pipe and has no pressure there. Electric valves let reservoir air directly to the brake cylinders.
Service brakes are nearly only dynamic brakes, adding air brakes at low speeds only. However at EB they are pneumatic only - I do not know what the reason for this design choice was, I'll have to ask someone driving them. Many things were experimental in those trains (and most of them haven't been done ever again xD)
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Post by zbx1425 Fri Apr 03, 2020 1:11 am

Thanks! Nice to know that!
My guess is that they thought air brake is more reliable and irrelevant to the power line status, as EMUs do not have individual levers for air brake and dynamic brake control.
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Post by Quork Fri Apr 03, 2020 10:38 am

Many EMUs, but not all. Classes 401 and 402 e.g. have the classic layout. Newer ICE EMUs don't have separate handles, but you still have some control; there's a button in the lever with which you switch between normal mode (dynamic brakes prioritised) and proportional mode (constant mix of dynamic and pneumatic). Holding it pressed results in pneumatic only, that's especially for defrosting the brake disks every now and then under snow conditions. And pressing it below 40km/h starts the "buffer stop mode", i.e. pneumatic only (you mustn't use dynamic brakes when closing up to something mechanical like a buffer, other vehicles or a derailer).
However that's irrelevant in the topic of EB, because in EB the vehicles always do the same, regardless of what position the dynamic brake lever is in or which program is active. Except for the three closely related classes mentioned above and very few other exots, that is using all/most available dynamic brake force and only "filling it up" with air brakes.
As I mentioned in a post before, locomotives tend to limit the dynamic brake in EB a bit further up the thread. I forgot to mention another important reason in this: We have classic buffers and couplers here in Europe. Because of this, under certain conditions pushing forces (i.e. braking with the front or accelerating with the back) have to be limited; in curves or switches which have a speed limit of 40km/h or less, the pressing force must not exceed 100kN. Since a locomotive doesn't know by itself whether those rules apply and since it can have a heavy goods train in brake regime G on the hook, you could end up with too high force; after all the dynamic brakes are effective nearly instantly while the cars in brake regime G will only reach their full braking force some 10-15 seconds later.
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Post by zbx1425 Fri Apr 03, 2020 12:48 pm

Quork wrote:As I mentioned in a post before, locomotives tend to limit the dynamic brake in EB a bit further up the thread. I forgot to mention another important reason in this: We have classic buffers and couplers here in Europe. Because of this, under certain conditions pushing forces (i.e. braking with the front or accelerating with the back) have to be limited.
Thanks a lot! I didn't know that before.
Most railways here is mainly divided into three genres, that is city subway, inter-city local railway and inter-city high-speed railway. There is clear boundaries between them.
For the subways, they are short EMU trains with tight-lock couplers, and most of the things I know are about them. Almost all of them cuts out the dynamic brake on emergency brake application. Some of them even lower the pantograph automatically as I said before. They don't have independent controls for dynamic brake and pneumatic brake.
For the local railway trains, they are long and are pulled by locomotives. The locomotives are quite similar to the others in the world, as they have automatic brake, independent brake and dynamic brake. They can be controlled independently. The dynamic brake on the locomotive does not do much for the heavy train, so in emergency scenerios the driver normally just throws the automatic brake in. But on some locomotives the dynamic brake gets cut out once the brake pipe is depressurized, which causes the accident i mentioned before.
FOr the high-speed EMU trains, a large number of them are directly purchased from Siemens, Kawasaki and Bombadier, so they are the same as the original trains, such as ICE3. The new truly "made in China" CRH380C, CR300AF and CR300BF trains might have different logics, but I don't know much of them.
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