Implement brake relay valve

Source/Documentation/Manual/physics.rst

@@ -2972,10 +2972,15 @@ MaxAuxilaryChargingRate and EmergencyResChargingRate.
 
 .. index::
    single: BrakePipeVolume
+   single: ORTSBrakeCylinderVolume
    single: ORTSEmergencyValveActuationRate
    single: ORTSEmergencyDumpValveRate
    single: ORTSEmergencyDumpValveTimer
    single: ORTSMainResPipeAuxResCharging
+   single: ORTSBrakeRelayValveRatio
+   single: ORTSEngineBrakeRelayValveRatio
+   single: ORTSBrakeRelayValveApplicationRate
+   single: ORTSBrakeRelayValveReleaseRate
    single: ORTSMainResChargingRate
    single: ORTSEngineBrakeReleaseRate
    single: ORTSEngineBrakeApplicationRate
@@ -2999,6 +3004,10 @@ MaxAuxilaryChargingRate and EmergencyResChargingRate.
   brake servicetimefactor instead, but the Open Rails Development team
   doesn't believe this is worth the effort by the user for the added
   realism.
+- ``Wagon(ORTSBrakeCylinderVolume`` - Volume of car's brake cylinder. This allows
+  specifying the brake cylinder volume independently of triple valve ratio.
+  This is useful when the cylinder is not directly attached to a triple valve,
+  e. g. when a relay valve exists.
 - ``Wagon(ORTSEmergencyValveActuationRate`` -- Threshold rate for emergency
   brake actuation of the triple valve. If the pressure in the brake pipe
   decreases at a higher rate than specified, the triple valve will switch to
@@ -3014,6 +3023,20 @@ MaxAuxilaryChargingRate and EmergencyResChargingRate.
   by the brake system.
 - ``Wagon(ORTSEPBrakeControlsBrakePipe`` -- Set to 1 for UIC EP brake: brake pipe
   pressure is electrically controlled at every fitted car.
+- ``Wagon(ORTSBrakeRelayValveRatio`` -- Determines the proportionality constant
+  between pressure as demanded by the triple valve and brake cylinder pressure.
+  This is achieved via a relay valve which sets BC pressure proportionally.
+  Relay valves may be installed to achieve higher brake cylinder pressures,
+  dynamic brake blending or variable load compensation.
+- ``Wagon(ORTSBrakeRelayValveRatio`` -- Same as above, but for the engine brake
+- ``Wagon(ORTSBrakeRelayValveApplicationRate`` -- Brake cylinder pressure application
+  rate achieved by the relay valve, if fitted.
+- ``Wagon(ORTSBrakeRelayValveReleaseRate`` -- Brake cylinder pressure release
+  rate achieved by the relay valve, if fitted.
+- ``Wagon(ORTSMaxTripleValveCylinderPressure`` -- Maximum cylinder pressure demanded
+  by the triple valve. For example, UIC distributors set maximum cylinder pressure
+  to 3.8 bar when brake pipe is below 3.5 bar, and further brake pipe discharging
+  does not increase cylinder pressure.
 - ``Engine(ORTSMainResChargingRate`` -- Rate of main reservoir pressure change
   in psi per second when the compressor is on (default .4).
 - ``Engine(ORTSEngineBrakeReleaseRate`` -- Rate of engine brake pressure

Source/Orts.Simulation/Simulation/RollingStocks/MSTSLocomotive.cs

@@ -1813,7 +1813,7 @@ public void DynamicBrakeBlending(float elapsedClockSeconds)
                 && ThrottlePercent == 0 && !(DynamicBrakeController != null && DynamicBrakeBlendingOverride && DynamicBrakeController.CurrentValue > 0))
             {
                 float maxCylPressurePSI = airPipeSystem.GetMaxCylPressurePSI();
-                float target = airPipeSystem.AutoCylPressurePSI / maxCylPressurePSI;
+                float target = airPipeSystem.AutoCylPressurePSI * airPipeSystem.RelayValveRatio / maxCylPressurePSI;
 
                 if (!DynamicBrakeBlended)
                 {

Source/Orts.Simulation/Simulation/RollingStocks/SubSystems/Brakes/BrakeSystem.cs

@@ -86,11 +86,11 @@ public abstract class BrakeSystem
         /// but for vacuum brakes it is a conversion to an internally used equivalent pressure.
         /// </summary>
         public abstract float InternalPressure(float realPressure);
-
         public abstract void Initialize(bool handbrakeOn, float maxPressurePSI, float fullServPressurePSI, bool immediateRelease);
         public abstract void SetHandbrakePercent(float percent);
         public abstract bool GetHandbrakeStatus();
         public abstract void SetRetainer(RetainerSetting setting);
+        public virtual void Initialize() {}
         public abstract void InitializeMoving(); // starting conditions when starting speed > 0
         public abstract void LocoInitializeMoving(); // starting conditions when starting speed > 0
         public abstract bool IsBraking(); // return true if the wagon is braking above a certain threshold