IEEE 1698:2009 pdf free download – IEEE Guide for the Calculation of Braking Distances for Rail Transit Vehicles
4.6.1 Propulsion removal
The propulsion removal component corresponds to the distance traveled during the period of time in whichtractive effort transitions from a net positive value to a zero (coast) value,usually on a jerk rate-limitedbasis.The resulting acceleration is typically assumed to be the average of the acceleration rate of thevehicle at the train speeds over the acceleration period.
Propulsion removal may consist solely of the transition of propulsion tractive effort from a positive value tozero. When emergency braking has been applied,simultaneous or overlapping transitions of decreasingpropulsion tractive effort and of increasing braking effort result in a net zero value at the defined end of thepropulsion removal component.The time duration of this component depends in part on whetherpropulsion is removed gradually via an intentionally jerk rate-limited control path,or removed, usuallymore abruptly, via a high-integrity backup control path.
Annex C describes and illustrates several practical examples of propulsion removal.
4.6.2 Dead time (coast)
The coast component corresponds to the distance traveled during the period of time during which tractiveeffort remains steady at a zero or near-zero value,beginning at the end of propulsion removal and endingwhen the braking rate has achieved a typical value of 10% of the value it will have during the brakingcomponent. The coast component may have negligible or zero time duration under certain conditions ofrelative timing of propulsion system power removal and brake system brake application, as illustrated inAnnex C.
4.6.3 Brake build-up
The brake build-up component corresponds to the distance traveled during the period of time during whichthe braking rate transitions from a typical value of 10% to the full value it will have during the brakingcomponent. Brake build-up may consist solely of the transition of braking rate from a typical value of 10%to the full value,or it may，where emergency braking has been applied,，include simultaneous oroverlapping transitions from propulsion to brake. The braking rate developed during brake build-up istypically assumed to be half the full braking rate of the braking component.The time duration of thiscomponent also depends on whether braking effort is applied gradually via a jerk rate-limited control path,or applied via a high-integrity backup control path such as a penalty brake application.
Annex C describes and illustrates several practical examples of brake buildup.
4.7 Guaranteed braking rate
4.7.1 Use and Nomenclature
As defined, the guaranteed braking rate component begins when the full deceleration rate is achieved, andends with zero speed.Braking rates are commonly stated in units of meters per second squared (m/s) ormiles per hour per second (mphps). ln computer calculations using industry standard train resistanceformulas,units in Newtons or pounds of force are used to describe the impact of braking on vehicle motion.All of these parameters are related through Newton’s Second Law as shown in Equation (1):
The deceleration that is described in this component of the braking distance model may include anallowance for other factors. These safety factors are described below.A typical safety factor is 35% and isbased upon the application of friction brakes only, applied through fail-safe or safety-critical circuits.
There is varying practice with this component of the braking model. Some authorities having jurisdictioninclude the safety factor in component H, the minimum braking rate，where some others separate thefunctions of braking and safety factor to recognize where different considerations are made.For thepurpose of this guide, the individual “safety factors” are presented here so that they are not confused withactual train braking.