Gearing in DMUs

[43021HST]

Something I was pondering the other day, how come modern DMUs for example class 159s, 185s, 165s etc are numbered in the 1xx series yet they are not of mechanical transmission, also how does the gearing system work on modern DMUs, becuse you dont see the driver now manually changing gears.

Does it work somehow with hydraulics?
Please dont go into long technical explanations I would like to understand it!

 

[ChrisCooper]

Hard to explain without being technical, but yes it is hydralics. Basically there are two parts, a torque converter which acts as the gears, and a fluid couplings which provides a direct driver at high speed. You hear the engine note drop when the changeover occurs, just over 40mph on a 75mph Sprinter. It's fully automatic with the driver having no control.

2XX wasn't really originally intended for DEMUs as much as SR DMUs, in the same way the SR EMUs were all 4XX, but when the 210s were introduced they were also numbered in the 2XX series to differentiate from the Sprinters. 1XX therefore has been used for all Mechanical and Hydralic units. Distinguishing between transmission types was never part of TOPs, hence why locos are lumped in together regardless of transmission. They are distinguished by power rating and power supply (DC or AC) though.

 

[driver9000]

The transmission is of a hydraulic nature. From 0-45 (some units differ with changeover speeds) the power is provided by a torque converter then once it has reached the end of its range the converter is emptied and the oil is transferred to a flywheel enabling the train speed to rise. The whole process is done automatically with no driver intervetion. They are numbered in the 1xx series as the power is delivered to the wheels by carden shafts and final drives rather than by traction motors.

Using lower notches can see the flywheel taking over before 45mph.

 

[jopsuk]

2XX wasn't really originally intended for DEMUs as much as SR DMUs, in the same way the SR EMUs were all 4XX, but when the 210s were introduced they were also numbered in the 2XX series to differentiate from the Sprinters.

Nice theory, but wrong- the Blue Pullmans were designated classes 251 and 261 (numbers never carried though), the prototype HST was orginally class 252 and the production HSTs were, for a while, numbered up as classes 253 and 254

 

[43021HST]

Hard to explain without being technical, but yes it is hydralics. Basically there are two parts, a torque converter which acts as the gears, and a fluid couplings which provides a direct driver at high speed. You hear the engine note drop when the changeover occurs, just over 40mph on a 75mph Sprinter. It's fully automatic with the driver having no control.

2XX wasn't really originally intended for DEMUs as much as SR DMUs, in the same way the SR EMUs were all 4XX, but when the 210s were introduced they were also numbered in the 2XX series to differentiate from the Sprinters. 1XX therefore has been used for all Mechanical and Hydralic units. Distinguishing between transmission types was never part of TOPs, hence why locos are lumped in together regardless of transmission. They are distinguished by power rating and power supply (DC or AC) though.

Helpful technical advice there, but I dont think 2xx series was for southern DMUs otherwise the class 159s would be 259s!

 

[Smudger105e]

It was meant the Hampshire Thumpers were 205's and the Oxteds were 207's, for example.

 

[Class172]

I see how hydraulics work now, but I don't understand is how modern mechanical transmissions work, such as on 172s.

 

[jopsuk]

they're pretty similar to a car (or rather, truck) automatic gearbox as I understand it, though with a seperate reversing mechanism so that the whole range is available in both direction.