Hi, does someone know how exactly do the brakes on this unit work? When I move the automatic brake lever just a little bit to the braking range, the brake pipe pressure lowers, the pressure in brake cylinders rises and the train starts to slow down. Makes sense so far. Now when I move the brake further into the braking range, the brake pipe pressure lowers even more (still makes sense), however the pressure in the brake cylinders falls back to zero and the train begins to brake with the electrodynamic brakes (based on the sound the train is now emitting). When I look outside, the brake pads can be seen applying even though there is no pressure in the brake cylinders, according to the barometer in the cab. The pressure in brake cylinder rises again only when coming to a halt. So how does it work? I would understand the unit begins to blend in ED brakes in the pneumatic brakes but then it doesn't make sense that there is no pressure in the brake cylinders, although the brake pipe pressure keeps lowering. Also it cannot mean the unit brakes only using EDB, because the brake pads can be seen appyling to the wheels. Thanks for any insight!
Most EMUs work this way. The brakes are blended though the BC needle will drop to 0 once dynamic braking begins. This happens so you can see transition from dynamic to straight air (just before coming to a stop). Check out the gauges on the LIRR and M9s.
Ok, so there is pressure in the brake cylinders, even though the needle reads zero? Another follow up question – what does the electro pneumatic cut out switch exactly do?
So the Arrow III brakes are set up as a normal triple valve brake with brake cylinder lockout / in-shot for blended dynamic braking. When you make a brake pipe reduction via the automatic brake valve, the air portion of the system responds the same as it would on unpowered push-pull equipment. If the TRACS computer system is functioning properly, it will detect the brake pipe reduction and force a bail-off of the brake cylinder pressure down to about 8 to 10 psi and substitute the lost air brake force with dynamic brake force from the motors. This way, the majority of the braking from 50 mph to 10 mph is accomplished through dynamic brakes, with the brake pads still applied to the wheel rims in the event that the pneumatic portion of the system has to take over in case of dynamic brake failure or emergency brake application. Above 50 mph, dynamic brake force falls off asymptotically as speed increases, and so if you are travelling at say 80 mph and make a full service brake application, you will see the brake cylinder jump up to about 30 psi to supplement the dynamic brake force; as speed falls towards 50 mph, you will see the BC pressure fall down towards zero as dynamic brakes assume the majority of the brake load. The dynamic brakes fade out starting around 10 mph, so as speed falls below that threshold, you will see the BC pressure rise back up to bring the train to a final stop. In regards to the in-game simulation showing zero PSI when dynamic braking is active between 10 mph and 50 mph while the brake pads are showing as applied, there is likely a disconnect between the brake pad animation and the simugraph behavior. The electro pneumatic cutout switch does exactly what is advertised; IRL, it cuts out the EP portion of the system. When the EP portion of the system is active, there is a low voltage control signal that propagates from the active brake valve to every car in the consist which ensures all brake applications are synchronized across the entire train (ie, all cars brake at the same time and at the same rate as the controlling car). When EP is cut out, the brakes behave as they would in a locomotive hauled train where the brake signal propagates via the reduction of the brake pipe, so the control car applies / releases first, followed by the second car, then the third car, and so on. As far as I am aware, this behavior is NOT simulated right now, so in-game, the EP system is always active and the cutout switch on the Arrows is just decoration.
Thanks for the detailed explanation! I tried the full service brake application at about 80 mph as you mentioned and indeed it played out exactly as you described. However, I still can't wrap my head around the action of the brake pads when braking between 50-10 mph. So you are saying, that the in this speed range, the majority of braking is done by EDB, but that the brake pads are still applied to some extent in case of for example EDB failure. But how does the train achieve this brake pad appliacation, when there is no brake cylinder pressure? Or is that what you meant by the disconnect between the brake pad animation and the simugraph behavior, meaning IRL there would be 8-10 PSI in the brake cylinders (with the reduced BP pressure ready to take over in case of an emergency)? As for the electro pneumatic cut out, I thought this would be the case, given that there is basically the same switch on the Koploper (although the switch there is simulated and that is the reason I thought it worked in a different way on the Arrow III – didn't consider the possibility of it not being simulated).
Short answer is that something is wrong, either with the simugraph or the animation. If the simugraph is calling for zero BC PSI between 50 and 10 mph, then it is incorrect. If the animation is showing the brake pads pressed against the wheels even when there is zero BC pressure, then the animation trigger is NOT tied to BC pressure; rather it is likely tied to whether you have the brake handle in a non-release position, which is also then incorrect. IRL, there is ALWAYS some BC pressure when the automatic brake is in the application zone of the handle.
