Add parameter for minimum speed of blended braking

Author: SteelFill

Source/Documentation/Manual/physics.rst

@@ -3344,6 +3344,7 @@ the following parameters will adjust the behaviour of air brakes:
    single: DynamicBrakeHasAutoBailOff
    single: ORTSDynamicBrakesHasPartialBailOff
    single: ORTSDynamicBlendingRetainedPressure
+   single: ORTSDynamicBlendingMinimumSpeed
    single: ORTSTrainDynamicBlendingTable
    single: ORTSDynamicBrakeReplacementWithEngineBrake 
    single: ORTSDynamicBrakeReplacementWithEngineBrakeAtSpeed
@@ -3358,6 +3359,9 @@ the following parameters will adjust the behaviour of air brakes:
   pressure which, when used in combination with ORTSDynamicBrakesHasPartialBailOff,
   will remain applied regardless of the blended dynamic brake force. This
   pressure is also the minimum pressure at which the blended braking system will activate.
+- ``Engine(ORTSDynamicBlendingMinimumSpeed`` -- Below the specified speed
+  (default units mph, default value 5 mph / 8 kph), local dynamic brake blending
+  will be disabled, allowing locomotive brakes to hold the train while stopped.
 
 Sometimes the train brake controller is capable to apply the dynamic
 brakes for the whole consist, usually as a first step before air brakes

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

@@ -421,6 +421,7 @@ public float OdometerM
         protected bool DynamicBrakeBlendingOverride; // true when DB lever >0% should always override the blending. When false, the bigger command is applied.
         protected bool DynamicBrakeBlendingForceMatch = true; // if true, dynamic brake blending tries to achieve the same braking force as the airbrake would have.
         public float DynamicBrakeBlendingRetainedPressurePSI { get; private set; } = -1.0f; // the amount of pressure that will always be retained in the brake cylinders during blended braking
+        public float DynamicBrakeBlendingMinSpeedMpS { get; private set; } = 2.25f; // below this speed, blended braking is disabled
         protected bool DynamicBrakeControllerSetupLock; // if true if dynamic brake lever will lock until dynamic brake is available
 
         public float DynamicBrakeBlendingPercent { get; protected set; } = -1;
@@ -1098,6 +1099,7 @@ public override void Parse(string lowercasetoken, STFReader stf)
                 case "engine(ortsdynamicbrakeshaspartialbailoff": DynamicBrakePartialBailOff = stf.ReadBoolBlock(false); break;
                 case "engine(ortsdynamicbrakereplacementwithenginebrake": DynamicBrakeEngineBrakeReplacement = stf.ReadBoolBlock(false); break;
                 case "engine(ortsdynamicbrakereplacementwithenginebrakeatspeed": DynamicBrakeEngineBrakeReplacementSpeed = stf.ReadFloatBlock(STFReader.UNITS.SpeedDefaultMPH, null); break;
+                case "engine(ortsdynamicblendingminimumspeed": DynamicBrakeBlendingMinSpeedMpS = stf.ReadFloatBlock(STFReader.UNITS.SpeedDefaultMPH, null); break;
                 case "engine(dynamicbrakesdelaytimebeforeengaging": DynamicBrakeDelayS = stf.ReadFloatBlock(STFReader.UNITS.Time, null); break;
                 case "engine(dynamicbrakesresistorcurrentlimit": DynamicBrakeMaxCurrentA = stf.ReadFloatBlock(STFReader.UNITS.Current, null); break;
                 case "engine(numwheels": MSTSLocoNumDrvWheels = stf.ReadFloatBlock(STFReader.UNITS.None, 4.0f); if (MSTSLocoNumDrvWheels < 1) STFException.TraceWarning(stf, "Engine:NumWheels is less than 1, parts of the simulation may not function correctly"); break;
@@ -1265,6 +1267,7 @@ public override void Copy(MSTSWagon copy)
             DynamicBrakePartialBailOff = locoCopy.DynamicBrakePartialBailOff;
             DynamicBrakeEngineBrakeReplacement = locoCopy.DynamicBrakeEngineBrakeReplacement;
             DynamicBrakeEngineBrakeReplacementSpeed = locoCopy.DynamicBrakeEngineBrakeReplacementSpeed;
+            DynamicBrakeBlendingMinSpeedMpS = locoCopy.DynamicBrakeBlendingMinSpeedMpS;
             DynamicBrakeMaxCurrentA = locoCopy.DynamicBrakeMaxCurrentA;
             DynamicBrakeSpeed1MpS = locoCopy.DynamicBrakeSpeed1MpS;
             DynamicBrakeSpeed2MpS = locoCopy.DynamicBrakeSpeed2MpS;
@@ -2034,9 +2037,14 @@ protected void CorrectBrakingParams()
         public void DynamicBrakeBlending(float elapsedClockSeconds)
         {
             // Local blending
+            if (airPipeSystem == null)
+            {
+                DynamicBrakeBlendingPercent = -1;
+                return;
+            }
             float autoDemandedPressurePSI = airPipeSystem.AutoCylPressurePSI * airPipeSystem.RelayValveRatio;
 
-            if (Math.Abs(SpeedMpS) > DynamicBrakeSpeed1MpS && airPipeSystem != null && autoDemandedPressurePSI > DynamicBrakeBlendingRetainedPressurePSI
+            if (Math.Abs(SpeedMpS) > DynamicBrakeBlendingMinSpeedMpS && autoDemandedPressurePSI > DynamicBrakeBlendingRetainedPressurePSI
                 && ThrottlePercent == 0 && !(DynamicBrakeController != null && DynamicBrakeBlendingOverride && DynamicBrakeController.SavedValue > 0))
             {
                 float target = (autoDemandedPressurePSI - DynamicBrakeBlendingRetainedPressurePSI) /