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Class 172

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Wyvern

Wyvern

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Kneedown said:
Torque converter changing to fluid coupling? Same as on 15X's and 170's? Which would make it Diesel Hydraulic wouldn't it?
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This is why the distinction is fuzzy. A torque converter system in theory doesn't have gears.
 
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ChrisCooper

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Actually a lot of torque converter systems do have gears. The Voith transmission on the DHMUs doesn't, but Voith transmissions on buses do (the MCW Metrobus and Scania N series double deckers often had Voith 3 speed + torque converter transmissions). Some DH locos have gears as well as a torque converter too. The "Sprinter" type transmission uses a torque converter and a fluid flywheel, the TC being the equivalent of changing up the gears, the fluid flywheel providing a top gear direct drive (like 4th gear on most cars, buses and trains with 4 or 5 speed boxes, 5th usually being an overdrive). There is no gear changing, just the TC is drained and the flywheel filled. Happens anywhere from around 40mph (75mph types) to I think 70 on the Turbostars and 175s (might not be as fixed on those those though, depending on conditions). Some types use multiple torque converters to give a wider range of speeds, filling and emptying them as needed. 180s and 185s are like that, are were some of the Hydralic locos. Automatic or Semi-Automatic mechanical transmission, like on the 1st Generation DMUs, original Pacers, Buses, and the 172s, still uses a fluid flywheel, as it works as a clutch to allow the engine to keep turning whilst the wheels are stopped, and to give a smooth pickup. Automatics on cars usually use a centrifugal friction clutch.
 
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ailsa

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Many automatic transmissions use a torque converter on the lower gears, but with a lock-up clutch for the higher gears for increased power transfer efficiency. I guess these are probably best described as hydro-mechanical transmissions, whereas the Voith 2-speed is purely hydraulic and will have a certain degree of slip, even in high gear.
 
Kneedown

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ChrisCooper said:
There is no gear changing, just the TC is drained and the flywheel filled. Happens anywhere from around 40mph (75mph types) to I think 70 on the Turbostars and 175s
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I don't fancy rummaging around in the garage for my old traction books, but if i remember rightly the official speed on 15X's and indeed 170's is 48mph, but in the real world it's between 43 and 50mph.
 
bronzeonion

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The chiltern ones better not have the same rock hard seats as the LOROL ones?! as I live on the line where they will stop and if they have got those seats Im going to be using the greenford line to get into london! all there turbos will be refurbed by then so yay
 
Wyvern

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So what is the difference between mechanical and hydraulic transmission?

Note the conventional clutch and gearbox used in a road vehicle has not proved reliable for railway work, except possibly at very low speeds. I've been told that with a road vehicle the rubber tyres provide damping to relieve the stresses,
 
tbtc

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bronzeonion said:
The chiltern ones better not have the same rock hard seats as the LOROL ones?! as I live on the line where they will stop and if they have got those seats Im going to be using the greenford line to get into london! all there turbos will be refurbed by then so yay
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I thought the plan was for the Greenford line to become a self contained Chiltern shuttle to Acton (or Ealing - apologies - can't remember), freeing up platform space at Paddington for FGW. This may have changed in the Cross Rail plans, of course
 
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The Planner

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The plan is for a bay at West Ealing and terminating there, there wouldnt be the paths once Crossrail gets a look in.
 
Wyvern

Wyvern

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Oracle said:
I have driven a diesel-mechanical shunter, and it had from memory a clutch facility by hand to engage the gears..probably air-operated. Gear selection was mechanical.
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I did add the proviso that it wouldn't be very fast. There have been geared steam locos as well.
 
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ChrisCooper

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Wyvern said:
So what is the difference between mechanical and hydraulic transmission?

Note the conventional clutch and gearbox used in a road vehicle has not proved reliable for railway work, except possibly at very low speeds. I've been told that with a road vehicle the rubber tyres provide damping to relieve the stresses,
Click to expand...

Right, the main purpose of a transmission is torque multiplication, torque being the turning force. At low speeds you want lots of torque at the wheels without putting too much load on the engine. At higher speeds you don't need as much torque, but want the wheels turning at high speed without overspeeding the engine. Internal combustion engines work best in a fairly narrow speed band, much lower than the range of speeds most vehicles over.
On a mechanical transmission it uses gears, usually 4, 5 or 6 which are at different ratios, each ratio being optimised for a different speed. Mechanical transmissions can be manual (driver controls clutch and gears), semi-automatic (driver selects gears, no clutch or automatic clutch) or fully automatic (driver does nothing).
Hydralics have no physical connection between the engine and the wheels, it is done by oil. The torque converter is set up so that when the output is stopped or turning at low speed, the torque is high, but when the output is turning at low speed, torque is low. It's like being on a bike and keeping in one gear. When you start you have to push down hard and put a lot of torque on the pedal shaft, but once at speed you push down less hard and the torque is lower. Instead of your feet on the pedals though, it's the oil. It's all fully automatic.
Some hydralic transmissions also have a mechanical gearbox too (mostly fully or semi-automatic). Semi and fully automatic gearboxes often have a hydralic clutch (known as a fluid flywheel or fluid coupling), which like a normal friction clutch allows the engine to remain turning when the wheels are stopped, and also absorbs shocks when changing gear, so it's not 100% straightforward.

In terms of the shunters, I don't know of any standard gauge shunters with manual clutches, but many classes (03s and 04s for example) have semi-automatic mechanical gearboxes and fluid flywheels. Some narrow gauge locos have manual clutches though. I've driven a 2ft gauge Simplex with a clutch and 2 speed manual gearbox.
 
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172001 is now back at Derby for full fitting out and delivery to LOROL.
 
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swt_passenger

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tbtc said:
I thought the plan was for the Greenford line to become a self contained Chiltern shuttle to Acton (or Ealing - apologies - can't remember), freeing up platform space at Paddington for FGW. This may have changed in the Cross Rail plans, of course
Click to expand...

The purpose of turning the Geeenford service into a shuttle (only as far as West Ealing in fact, which gets a new west facing bay) is solely to prevent conflicts at the flat junction at West Ealing, when the full Crossrail 10 tph is running on the reliefs along with other GW DMU services. It isn't really about freeing up platform capacity at Paddington, that'll happen anyway due to services transferring onto Crossrail.

I don't recall any proposals about transferring it to Chiltern though - what advantages would that give?
 
Voyager 2093

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Hmm sounds interesting. No gens or rail sites have posted news on 172 001 leaving Derby. Last I heard it had returned to Derby.
 
Voyager 2093

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Could have been a test run, however that's what Old Dalby is for. This is really interesting. Did you not have a camera on you to take a picture.
 
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The Planner

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LOROL 172s are due to do milage accumalation on the WCML slows to Bletchley and back. LM ones on Stourbridge to Whitlocks End/Stratford.
 
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