Trains accelerate incredibly slowly and often have a single gear that is optimised for high speed. Similar to trying to pull away in your car in too high of a gear this makes trains really slow and takes along time for them to hit their high speed.
Most cars will often have 4 (for very old cars) – 6 gears to keep acceleration smooth and fast whilst still being efficient at high speed but trains don’t.
I get that electric motors have all of the torque available at low RPMs whilst ICE only have full power at a high rpm but wouldn’t gears still allow trains to get to higher speeds quicker?
In: Engineering
Modern locomotives are electric. The diesel engine provides power to the the main generator which then goes through a rectifier and then gets sent to the traction motors (wheels) the engineer controller the speed through the use of notches or speeds 1-8. Even in 8th notch the engine is hardly over 900 rpm. 903 rpm iirc
The electric trains around here definitely have more than one gear – or at least something that *sounds* like gears. Perhaps the sound is something to do with switching electrical circuits for a similar effect, rather than actually changing the gear ratio, though…
I wish I could find a youtube video or something of them to share, but would you believe, people don’t seem to upload many videos of naff trains leaving stations 😛
EDIT: not a great sound recording (lots of background noise and there’s a diesel at the same time) but you can year the whine of the electric motor rising then cutting to a lower pitch and rising again several times: https://www.youtube.com/watch?v=LQu-nu3tbKU I tried counting how many “gears” the trains around here have a few times and it’s at least double figures of that sawtooth pitch thing…
A locomotive does not have a transmission in the same sense as a car. Locomotives in general are Diesel-Electric. This means that the wheels are not mechanically connected to the Engine. The wheels are connected to traction motors which provide the motive force. The motors are themselves powered by the electric power generated by the massive generators which are run by the diesel engine. The reason for this as follows.
A locomotive is typically generating about 4000-5000 HP. An IC Engine (diesel) producing this kind of power is huge including the main drive shaft. Now the wheels which are roughly the size of a truck wheel rotate at a fairly high RPM in order to move linearly at 60-90 MPH. The massive drive shaft which cannot rotate at very high speeds due to the immense mechanical forces involved. So it will need a massive transmission system to match the high speeds needed at the wheels which is not viable. This is the reason why Locomotives are Diesel-Electric. The other huge advantage of this is that it enables easy coupling of multiple locomotives to run bigger and bigger trains with one point of control. All the traction motors on the multiple locomotives run off the same electrical BUS to which all the Locomotive engine/generators are contributing electrical energy to.
Diesel trains, apart from diesel-electrics which have essentially the same transmission as AC or DC electric trains, have gearboxes. In most cases the gearboxes are fluid-filled torque converters with automatic gearchange from one or more torque ratios to direct drive ratio (equals top gear) and are known as diesel-hydraulic.
Some older trains were diesel-mechanical with manual gearchange. These were nearly all multiple-units as opposed to locomotives, and had a clutch-less planetary gearbox controlled through electro-pneumatic valves. There might be some of these left around the world, but the UK withdrew them about 15 years ago.
Latest Answers