Elvas Tower: The Quest for Realistic Braking (quick service) - Elvas Tower

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The Quest for Realistic Braking (quick service)

#1 User is offline   jdilworth 

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Posted 21 March 2018 - 03:58 AM

Hey gang,

I'd like to ask about the possibility of the application of a quick service feature to the air brake model OR uses. At the moment, first service automatic brake applications translate into a 2.5x ratio in the rail car brake cylinders, which is higher than they should be when matched with real world examples. The quick service feature has been a requirement on all control valves since the late 1800s. I may have written about this before, but I think, from a realism standpoint, it is something that should be part of the braking model in OR. As trains got longer, the length of time to get the brake reduction signal from the head end to the tail end of the train was significant enough to cause run ins. So, they devised a quick service inshot valve to help correct the problem. When a reduction of 6 lbs or less is made from the head end, the quick service valve will trigger an immediate 6 lb reduction in the brake pipe, and put about 10-12 lbs of pressure into the brake cylinder (note: This is not a 2.5x ratio). The speed at which this happens is significant because the control valve only needs to detect a 1 lb reduction in the brake pipe to trigger quick service (6 lb reduction in brake pipe). That means that the overall brake pipe reduction will happen very quickly down the length of the train, creating a softer first application and reducing run ins. If the engineer moves the automatic brake into the service zone, beyond first service, the standard 2.5x ratio applies. So, for example, if they make a minimum reduction of 6 lbs, the quick service reservoir empties into the cylinder, producing about 10-12 lbs of pressure, and equally draws 6 lbs from the brake pipe, speeding the overall brake pipe reduction time. When the engineer moves the automatic brake into the service zone and makes a further 2 lb reduction, the standard 2.5x ratio applies to the car control valve. In this case, the extra 2 lb reduction would make an 8 lb reduction, and the car brake cylinder pressure would move from 10-12 lbs to 20 lbs. A further reduction of 2 more pounds, would produce 25 lbs in the cylinder, and so on.

From a train handling standpoint, the existing braking model makes it almost impossible to have an air gradient in the train. Let's assume the quick service feature is working. You make a minimum reduction of 6 lbs, and the brake pipe drops from 90 to 84 psi. You release the brake and the train recharges. Now, lets say the head end is charged up to 90 psi, and 60 cars back its still 87 psi. You make a minimum reduction again. In the current MSTS/OR braking model, the rear will equalize to 84 lbs just like the head end, which isn't correct. If the rear is 87 psi, and you make a first service reduction again, quick service feature will be triggered, and the rear would immediately drop 6 lbs, making it 81 psi at the rear. To help clarify my point, I'm quoting some material written by Al Krug a number of years ago:

-----------------

"Quick Service Reservoir (Inshot)
Because, during a normal service application, all the brake pipe air has to vent thru the loco's control valve, it takes a long time to get the brakes set through out the train. The pressure first drops near the front of the train and then drops further and further towards the rear. This causes the brakes to set up on the front part of the train before they set on the rear portion. This causes the rear end to run into the front end (slack action).

So some smarty comes up with the idea of modifying the triple valve on the cars so that when a car first senses a drop of pressure, it opens a passage from the brake pipe to a small reservoir (a third reservoir called a "quick service reservoir"). This reservoir is sized such that it has the proper volume in relation to the car's brake pipe volume that filling it with air from the brake pipe will reduce the brake pipe 6 psi. That means when I make anything up to a 6 psi reduction, 6 psi worth of it is done at each car. This results in a faster (but not fast enough to trigger emergency) more even application of the brakes thru the train. It only works the first time, however, since after that the reservoir is filled and remains so until the brakes are released.

The Quick Service feature is an 1895 requirement of the Master Car Builders' Association (now called the AAR). Early triple valves didn't have Quick Service. The feature was first introduced with the K freight brake of 1900 (or 1901) and has been a requirement for all braking systems since. Triple/control valves accomplish quick service in one of three ways, depending upon the model of the valve: put the air into the brake cylinder (K does this), throw the air away (AB/ABD does this), or save it in a reservoir for use if an emergency is called for later (a modification to ABD/ABDX for some designs of TOFC, auto rack, articulated container cars, and others). This third method is the reservoir mentioned.

It takes only about 1 to 1½ psi pressure differential across the face of the triple/control valve operating piston to move it. Once it moves, it goes to Quick Service, with no choice offered and reduces the brake pipe by 6 psi. If the engineer makes an initial reduction that is greater than 6 psi, Quick Service action within the valves will be bypassed. If he makes one that is less, the valves on the cars will make sure it becomes a 6 psi reduction. The Inshot Piston is a device inside the Emergency Portion of an AB control valve and it is used to regulate the flow of air into the brake cylinders into two stages during an emergency application in order to get a modicum of control over slack action in the train during the emergency application."

http://www.railway-t...an-freight.html


Is this something the OR team can consider adding? Every brake control valve for the past 120 years has had this feature, so it would be cool to have for more realistic operation. Thoughts?

Thanks,
Jason

#2 User is offline   jared2982 

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Posted 22 March 2018 - 02:26 AM

I also made an observation about how OR recharges the brake pipe from a minimum reduction (first service). From the F5 screen OR is using a portion of the Emergency reservoir to recharge the system from first service. While this is a feature that control valves have ,accelerated service release, this is not correct IIRC. A portion of the Emergency reservoir air is not used to release the brakes after a minimum reduction. A reduction of at least 10lbs is required before Emergency reservoir air is used to accelerate the release of the brakes.

#3 User is offline   Tyler Bundy 

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Posted 22 March 2018 - 06:20 PM

Jason, that's a good explanation of the concept, and I too support this addition if the OR team sees fit.

Since we're on the topic of "Quick", I remember that triple-valves on North American equipment also feature a quick release as well (this might be what Jared is talking about). I lack the specific details of such operation, but it seems to work in reverse of the "quick service" feature. Once the triple valve senses a rise in brake pressure, it should automatically release the pressure of it's brake cylinder, and feed a little air back into the brake pipe. The term I've heard used in both instances is "Propagation". Each car propagates the air signal to the next, causing a faster service/release than would be possible otherwise.

The quick release feature I mentioned above is the reason why you should never "bottle the air" on a consist (retain air pressure on an isolated consist without an engine attached). A leaking triple-valve on a car can send a false release signal to the car next to it, which proceeds with a full release and propagates that signal down the line until all brakes are released. This can happen if you close the angle cock on a consist that's just been put into emergency. Too much air leaking from a reservoir through the triple-valve can provide the 1-2 psi rise to the next car, and once the propagation starts, it pretty well feeds itself.


Some of you folks know more about this than I do, but I thought that the quick release feature might fit well with the quick service discussion.


Tyler

#4 User is offline   jdilworth 

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Posted 24 March 2018 - 11:05 AM

Hi know that Al Krug talks about the accelerated release feature in the same article I referenced in my first post. ( http://www.railway-t...an-freight.html ).

He doesn't say anything about how much of a reduction is required before it draws from the emergency reservoir to assist in the recharge. I'll need to research that myself. Logically thinking though, it would be assumed that if you are releasing the brakes, you aren't likely to throw it in emergency shortly thereafter, so maybe there is no minimum required brake pipe reduction before it uses air from the emergency reservoir to recharge the brake pipe. I'll have to do some digging and see if I can find out more.

Cheers,
Jason

#5 User is offline   jared2982 

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Posted 01 May 2018 - 11:54 AM

Has the OR team looked into this yet?

#6 User is offline   R H Steele 

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Posted 01 May 2018 - 12:36 PM

Until development adds the features in discussion, you might try these parameters --- they are quite responsive, maybe a little too much so.
Both the Std_Eng_ES44AC.inc and the Std_Loco_Brakes.inc files are contained in the Common.inc** folder found in the trainset.
**Note >>> credit for the name "Common.inc" goes to Dave Nelson >>> please read this thread >>> http://www.elvastowe...ds/page__st__50
Thanks, Dave!!
Engine Brake native ORTS parameters are between the ORTSDiesel Engine block and the ORTS MaxTractive Curves. Brake section used in Loco (wag section) follows
The particular engine is for a Gevo, but I'm using identical parameters for all locomotives at present, until I do more testing and adjustments.

Comment ( Standard ORTS Diesel Engine for GE ES44AC,C45ACCTE,GEVO  )
Comment ( Performance Ratings == 4400HP == 166000lb CTE == 183000lb MTE )
Comment ( include ( "..\\..\\Common.inc\\Locomotives\\Std_Eng_ES44AC.inc" ) )

ORTSDieselEngines ( 1
		Diesel(
			IdleRPM ( 315 )
			MaxRPM ( 1050 )
			StartingRPM ( 225 )
			StartingConfirmRPM ( 365 )
			ChangeUpRPMpS ( 90 )
			ChangeDownRPMpS ( 55 )
			RateOfChangeUpRPMpSS ( 35 )
			RateOfChangeDownRPMpSS ( 25 )
			MaximalPower ( 3281.079kW )
			IdleExhaust ( 0.1 )
			MaxExhaust ( 0.2 )
			ExhaustDynamics ( 0.5 )
			ExhaustDynamicsDown ( 0.5 )
			ExhaustColor ( 206B787D )
			ExhaustTransientColor ( 40212324 )
			DieselPowerTab (
  				0  	0
				315  	0
				407  	410135
				499  	820270
				591  	1230405
				683  	1640540
				775  	2050674
				867  	2460809
				959  	2870944
				1050  3281079
			)
			DieselConsumptionTab (
				0	0
				315  13.6
				1050 586.7
			)
			ThrottleRPMTab (
				0   315
				12.5  407
				25  499
				37.5  591
				50  683
				62.5  775
				75  867
				87.5  959
				100  1050
			)
			DieselTorqueTab (
				0 	0
				315  92301
				1050  738405
			)
			MinOilPressure ( 20 )
			MaxOilPressure ( 90 )
			MaxTemperature ( 120 )
			Cooling ( 3 )
			TempTimeConstant ( 720 )
			OptTemperature ( 71 )
			IdleTemperature ( 55 )
		)
	)
	ORTSMainResChargingRate ( 0.237 )
	ORTSBrakePipeChargingRate ( 40 )
	TrainPipeLeakRate ( 0.0833 )
	ORTSEngineBrakeReleaseRate ( 38 )
	ORTSEngineBrakeApplicationRate ( 34 )
	ORTSBrakePipeTimeFactor ( 0.003 )
	ORTSBrakeEmergencyTimeFactor ( 0.1 )
	ORTSBrakeServiceTimeFactor ( 1.009 )
	ORTSMaxTractiveForceCurves ( 0 ( 0 0 50 0 )
			.125 (
				0 101753
				0.3 101753
				1 30731
				2 15365
				5 6147
				10 3071
				20 1536
				50 616 )
			.25 (
				0 203506
				0.61 203506
				1 122940
				2 61465
				5 24588
				10 12294
				20 6147
				50 2460 )
			.375 (
				0 305259
				0.91 305259
				2 138296
				5 55318
				10 27664
				20 13830
				50 5531 )
			.5 (
				0 407013
				1.21 407013
				5 98343
				10 49172
				20 24588
				50 9834 )
			.625 (
				0 508766
				1.51 508766
				5 153662
				10 76831
				20 38413
				50 15365 )
			.75 (
				0 610519
				1.82 610519
				5 221274
				10 110637
				20 55318
				50 22128 )
			.875 (
				0 712272
				2.12 712272
				5 301176
				10 150586
				20 75295
				50 30119 )
			1 (
				0 814025
				2.42 814025
				5 393372
				10 196686
				20 98343
				50 39337 )
		)
	ORTS  (	ORTSWheelslipCausesThrottleDown ( 1 )
			ORTSEmergencyCausesThrottleDown ( 1 )
	)


Locomotive Brake Parameters (in wag section)

Comment ( Standard Diesel Locomotive Brakes )
Comment ( include ( "..\\..\\Common.inc\\Locomotives\\Std_Loco_Brakes.inc" ) )

	BrakeEquipmentType ( "Handbrake, Triple_valve, Auxilary_reservoir, Emergency_brake_reservoir" )
	BrakeSystemType( "Air_single_pipe" )
	MaxBrakeForce( 178kN )
	MaxHandbrakeForce ( 57.2kN )
	NumberOfHandbrakeLeverSteps( 100 )
	EmergencyBrakeResMaxPressure( 110 )
	TripleValveRatio( 2.5 )
	EmergencyResVolumeMultiplier ( 1.461 )
	MaxReleaseRate( 22.2 )
	MaxApplicationRate( 13.9 )
	MaxAuxilaryChargingRate( 20 )
	EmergencyResCapacity( 1.792ft^3 )
	EmergencyResChargingRate( 20 )
	BrakePipeVolume ( 0.307ft^3 )
	BrakeCylinderPressureForMaxBrakeBrakeForce( 70 )


The actual engine include file in the OpenRails folder


include ( "..\\BNSF6642.eng" )
Wagon (
	include ( "..\\..\\Common.inc\\Locomotives\\Std_TypeF_Coupler.inc" )
	include ( "..\\..\\Common.inc\\Locomotives\\Std_Loco_Brakes.inc" )
	ORTSAdhesion ( ORTSCurtius_Kniffler ( 7.5 44 0.161 0.7 ) )
	ORTSAdhesion ( ORTSSlipWarningThreshold ( 70 ) )
	ORTSBearingType ( Roller )
	ORTSDavis_A ( 1976.76 )
	ORTSDavis_B ( 62.0917 )
	ORTSDavis_C ( 8.510148 )
	Comment( == Assumptions -Locomotive diesel/electric - speed - 65mph (105km/h), Roller Bearing, 6 axles, frontal area - 14.8m2, Wagon Weight - 188.7 ton (metric), Drag 1.0 == Davis speed: 53km/h,  RMS Error: 23.19N,  Max Error: 41.61N @ 105km/h )
)
Engine (
	Effects (
		DieselSpecialEffects (
			Exhaust1 (
			0.1 5.076 -2.945
			0 1 0
			0.15
			)
		)
	)
	include ( "..\\..\\Common.inc\\Locomotives\\Std_Eng_ES44AC.inc" )
)


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