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Re: When Will the Feds Stop Outlawing Railcars Used By the Rest of the World?
Author: Dr Zarkoff
Date: 07-15-2016 - 10:11
>> Can an electric light rail vehicle, say a Citadis, stop faster than a SMART Kinki Sharyu DMU?
> I don't know the braking equipment of the DMU, but an educated guess would say that the Citadis can stop faster from the same speed.
Any braking system which relies on the wheel-rail interface to do its thing is ultimately dependent on the static friction between the wheels and rails, which is a function of the car's weight on the rails (the definition of adhesion). Sprag brakes (track brakes) take advantage of the same weight but operate via separate interface, the track brake shoes rubbing on the rails.
All braking systems are designed with so that the total retarding force doesn't exceed adhesion, and it's a case of how close to adhesion you want to operate. Too close to the limit, and there will be excessive loss of static friction, meaning wheel slide, and the loss of almost 50% of braking power.
I would expect that the two cars mentioned above have been designed with a 100-110% braking ratio, which has been a typical figure for light rail and passenger trains for decades. This means both would be able to decelerate at the same rate.
> I don't know the braking equipment of the DMU, but an educated guess would say that the Citadis can stop faster from the same speed.
Any braking system which relies on the wheel-rail interface to do its thing is ultimately dependent on the static friction between the wheels and rails, which is a function of the car's weight on the rails (the definition of adhesion). Sprag brakes (track brakes) take advantage of the same weight but operate via separate interface, the track brake shoes rubbing on the rails.
All braking systems are designed with so that the total retarding force doesn't exceed adhesion, and it's a case of how close to adhesion you want to operate. Too close to the limit, and there will be excessive loss of static friction, meaning wheel slide, and the loss of almost 50% of braking power.
I would expect that the two cars mentioned above have been designed with a 100-110% braking ratio, which has been a typical figure for light rail and passenger trains for decades. This means both would be able to decelerate at the same rate.
