What is this cable attached to the bearing?

[aegrotatio]

What is this cable attached to the bearing on a SuperLiner?

[Wizlish]

You can tell from the little 'teeth' milled on the bearing shell -- it's a rotation (speed) sensor.  Probably used here to detect wheelslide in braking.

[D.Carleton]

Wizlish is correct, it is a proximity sensor used to detect if the wheel is locking up during breaking. We refer to them as 'electronic decelostats' to differentiate from mechanical decelostats.

[erikem]

I'm guessing that it is a Hall-effect sensor which detects whether or not the steel toth is in close proximity to the sensor. Made use of one about ten years ago to make an electronic odometer.

[Wizlish]

Here is a (non-typical-Wikipedia) description of the Hall-effect sensor for anyone not 'in the know' who wants to know how it works:

http://www.electronics-tutorials.ws/electromagnetism/hall-effect.html

 

[oltmannd]

It's function is to provide "anti-lock" brakes for a passenger car.  Decelostat systems came into widespread use in the streamliner era to accomodate higher speeds with the same block lengths.  The systems regulate the air pressure when one axle starts to slip during braking by backing off the air pressure to the brake cylinders.  It figures this out by comparing the speed of each axle.  Locomotives have similar devices on a gear on the end of each traction motor shaft to measure slip/creep/slide.

[blue streak 1]

You see this gear setup on digital anti skid sensors for braking.  Antiskid brakes are hydraulic.

Analog brakes on older airlines use a generator on wheel for anti- skid.  Not as accurate.

[aegrotatio]

Thanks for all the information. These were on pretty much all the Auto Train SuperLiners in Lorton a couple years ago.

 

I think it's worth mentioning that most Auto Train locomotives are rehabbed P40s that use freight-style brake systems.  This might shed some light on why these sensors are installed.