darwins, on 29 April 2023 - 11:55 AM, said:
Proportional valves are only normally found on locomotives. In fact they are standard on modern locomotives - they control the brake cylinder pressure in proportion to reductions in the train brake pipe pressure. They allow the loco brake cylinder to have any appropriate value, which may be outside of that normally achieved with a triple valve, including values greater then the train brake pipe value. They also allow locomotive air brakes (or steam brakes) to be operated by train vacuum brakes.
What you are describing for freight cars is something called load compensation. This is common on modern freight wagons around the world. (It is also used on most passenger trains now, but since we don't have varying passenger loads in Open Rails, we don't need to worry about this for passenger cars.) This should already be possible in OR using the load animation features
EmptyMaxBrakeForce ( x ) and FullMaxBrakeForce ( x ) something like this example from
https://www.coalston...sics/animation/ and in Chapter 9 of the testing manual.
ORTSFreightAnims
(
WagonEmptyWeight( 28.75t ) Comment( 57500lbs )
EmptyMaxBrakeForce ( 29.892kN ) Comment (Assume empty weight of 62.41t us)
FreightAnimContinuous
(
FreightWeightWhenFull( 42.725t )
FullMaxBrakeForce ( 190.771kN ) Comment (Assume full weight of 71.475t us)
)
)
In real life there were two different ways of doing this.
Modern carriages and wagons have a continuously variable brake force depending on load. This is what I understand is described by the above.
Older goods wagons simply had a lever which could be moved to either "Loaded" or "Empty". These had only two possible values of brake force regardless of the load they were carrying. I am not quite sure how this kind of wagon should be modelled in OR.
Sorry mate, proportional valves
are used on freight cars. Yes, I am talking about load compensation, but proportional valves are how load compensation is achieved on modern American freight stock. It's not an identical setup to locomotives as the use case is generally to produce a lower pressure, not a higher pressure, than usual. But it's there.
For those curious, the way this works is that a car detected to be empty (how this detection works [and sometimes doesn't work] is a whole topic on its own) will divert air away from the brake cylinder toward a dummy reservoir and a proportional valve. The proportional valve will limit the pressure going to the brake cylinder line to a proportional fraction of the pressure coming out of the control valve (usually 60%, 50%, or 40% depending on the empty weight of the train car). The dummy reservoir is there to ensure that the same amount of air is used when the car is empty as when it's loaded, regardless of the reduction in the brake cylinder pressure. The result is that the control valve is fooled into 'thinking' (for example) 64 psi of brake cylinder pressure has been applied, while the brake cylinder pressure is actually only 32 psi. Half the pressure, roughly half the braking force. Easy way to automatically reduce the brake force.
https://i.imgur.com/r5c93fR.png
Also, using Empty/FullMaxBrakeForce is a terribly unrealistic solution, this setup results in the same brake cylinder pressure producing completely different forces. The only way that can happen is if two different brake cylinders are used which is a very old-fashioned way of doing things, which isn't the kind of content I work on. I fully recognize most content creators just live with this, but I don't. The best option right now, and the option I use, is to change the triple valve ratio in the wagon file in order to give lower brake cylinder pressures for the same brake pipe reduction. This causes all sorts of other issues, so it's really a bodge more than anything. That's why proportional valves should be implemented for both loco brakes and wagon brakes.
https://i.imgur.com/wpuA4LY.png
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