Elvas Tower: Retardation Control - Elvas Tower

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#1 User is offline   darwins 

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Posted 07 November 2022 - 01:19 AM

Can I make a request for Retardation Control to be added to the OR braking system?

Retardation Control is breifly described here.

It is (or was) used with EP braking to limit the maximum rate of deceleration. This was widely used on trains with EP braking before modern electronic WSP (wheel slide protection) systems became available.

In brief the system works like this:

If the driver makes a full service application

EP valves admit air from the Main Reservoir Pipe to the brake cylinders until either Actual Deceleration Rate = Set Retardation Rate or Brake Cylinder Pressure = Main Reservoir Pipe Pressure

(For this reason the EP brake should not be left in the 'Full Service' position when the train is stationary!)

As the speed of the train is reduced then less brake force and less brake cylinder pressure is needed to maintain the deceleration rate.

If Actual Deceleration Rate > Set Retardation Rate then air is released from the brake cylinder until Actual Deceleration Rate = Set Retardation Rate again.

The retardation control normally only operates during EP (service) braking and not when the Automatic Air Brake is used alone or during Emergency Braking.

For London Underground trains the maximum deceleration rate with the EP brake was set at 2.6 mph/s ( 1.16 m/s^2 ) https://www.railways...ensPark1949.pdf

(Reading the OpenRails units of measure it seems as though rate of change of speed / acceleration / deceleration is not defined, although I thought some cabviews have accelerometers.)

Similar to

ORTSWheelBrakeSlideProtection ( 1 )
ORTSEmergencyBrakingDisablesWSP ( 0 )

I would think that Retardation Control could be defined by something like

ORTSEPBrakeRetardationControl ( 1 )
ORTSEmergencyBrakingDisablesRC ( 1 )
ORTSEPBrakeMaxRetardation ( 1.16m/s^2 )

#2 User is offline   Weter 

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Posted 07 November 2022 - 06:48 AM

Hello.
Great, You're still planning new features.
Thoughts aloud: for metro, ED brakes are more suitable. Furthermore with recuperation possibility.
Since EP has graduated release, drivers, when have no automatic retardation control are doing, what You've said by hand (decrease BC pressure before complete stop)
This operation is very prototipical in train-simulators.

#3 User is offline   Coolhand101 

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Posted 07 November 2022 - 08:13 AM

Interesting! I never heard of this feature on BR EMUs built in the 60s/70s. I have heard of something similar for the Blue Pullman EMU.

Thanks

#4 User is offline   Coolhand101 

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Posted 07 November 2022 - 08:35 AM

View PostWeter, on 07 November 2022 - 08:17 AM, said:

Wasn't Pullman diesel-propelled?


Yes it was. Here you go = D.E.M.U!

Thanks

#5 User is offline   darwins 

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Posted 07 November 2022 - 09:00 AM

View PostCoolhand101, on 07 November 2022 - 08:13 AM, said:

Interesting! I never heard of this feature on BR EMUs built in the 60s/70s. I have heard of something similar for the Blue Pullman DEMU.

Thanks


I have only just came accross the fitting of it to BR EMUs in late 60s and early 70s - I need to keep track of my web browsing to find out where it was mentioned. More information definitely needed here.

The Blue Pullman is a logical place for it to work with EP brakes, though the description provided on Railcar.co.uk does not suggest retarders

Quote

In the high speed range the brake pressure was automatically increased to compensate for the lower coefficient of friction of the cast-iron shoes when operating at high speeds. The changeover from high speed to normal speed braking, and vice-versa, was entirely automatic and was controlled by a valve energised by current from the speedometer generator. The de-luxe Pullmans were the first train to be fitted with two-stage EP braking.


Simply it says that a higher brake cylinder pressure was applied above a certain speed and a lower one below that speed. Another braking possibility that we do not yet have in OpenRails!

This same idea of two-stage braking, but with twin pipe air brakes was later used on the HSTs.

#6 User is offline   darwins 

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Posted 07 November 2022 - 10:18 AM

View PostWeter, on 07 November 2022 - 09:18 AM, said:

This reminds me an auto-regime devices for BC pressure adjustment on freight and EMU cars, where load is to be significantly varied during trip (so no possible to tune each car's distributor). So this device is for load's mass-proportional BC pressure, not speed-proportional. On EMU, it works periodically, measuring load, when driver closes EP-operated doors: it adjusts BC pressure and holds this setting, until new door closure on next stop (after passengers density in car have been changed again)



Load compensation is common on modern passenger vehicles, just as on modern freight vehicles. It can already be modelled in OpenRails:

ORTSFreightAnims
(  EmptyMaxBrakeForce ( 29.892kN )

FreightAnimContinuous
(  FullMaxBrakeForce ( 89.676kN ) ) )


At the moment this is only useful for freight wagons, as there is no variation in the load of passenger trains in OR depending on the quantity of passengers and luggage.

The older Mercury Retarders provided load compensation as well as speed compensation. A more heavily loaded car would require a higher brake force to achieve the same deceleration rate.

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