On Thu, 17 Aug 2017 19:52:19 -0700 (PDT), Christopher Tidy
wrote:

Am Mittwoch, 16. August 2017 22:52:01 UTC+2 schrieb :
The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling.

Interesting comment. I can see this being a key problem. Just thinking about it, how do diesel engines scale? I mean, the bell housing on a small car engine has a diameter of what? 30 cm? And on a locomotive engine maybe 100 cm? So you can have something like a 25 cm diameter clutch in a car and a 85 cm diameter clutch in a locomotive? Let's assume it's a single plate clutch for now.


There is no clutch on the usual a diesel-electric drive. Just an
rheostat to control the electricity going to the motor(s). A
diesel-electric vehicle often has a number of motors.

Taking this a bit further, if you have maximum engine torque and 0 rpm at the wheels, how much power are you briefly sinking into the clutch? Maybe 50 kW in the car and 1500 kW in the locomotive? Which means you have 11 times the clutch area and 30 times the power. Following this logic, I can see how clutch scaling is going to max out at about the size of a large truck, and on top of that, trains accelerate quite slowly. The heating might not be so brief.


The motor torque is normally applied directly to the driven wheel.

Nice thought, Randall.

Chris