Chiltern class 172 - Change to hydraulics transmission?

superkev · 10 Jan 2019

hexagon789 said:
Always interesting to read, and where I get much if my acceleration times info from. It does show how superior 172s are off the mark compared to a 168/170 etc.

I've always hoped rail express would do comparative 0-60 timings of the 350hp and 400hp varieties of class 158. I'm sure the lightweight 158/ 400hp would outpace a 172.
The clerks who run Northern probably dont even know they have potential flyers on there hands.
K

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XCTurbostar · 10 Jan 2019

Let’s not also forget that the figures described a chiltern unit - 172103 doing the tests with an Ecoshift Map. If the 172s were re-mapped for performance, they would probably be even faster.

hexagon789 · 10 Jan 2019

superkev said:
I've always hoped rail express would do comparative 0-60 timings of the 350hp and 400hp varieties of class 158. I'm sure the lightweight 158/ 400hp would outpace a 172.
The clerks who run Northern probably dont even know they have potential flyers on there hands.
K

I had actually thought they had done both hp variants of 158s, need to look at that.

I'm not sure it would significantly improve their acceleration, the 400hp was more for hill-climbing so I think it would simply mean they can maintain speed up steeper gradients than either of the 350hp 158 types.

squizzler · 10 Jan 2019

I don’t buy the argument that an absence of coasting in the 6speed transmission will be materially detrimental to fuel economy. Ask a motorist: you should never put your car in neutral to coast. Rather you can choose a higher gear to reduce engine revs which surely the zf box would do.

Bletchleyite · 10 Jan 2019

squizzler said:
I don’t buy the argument that an absence of coasting in the 6speed transmission will be materially detrimental to fuel economy. Ask a motorist: you should never put your car in neutral to coast. Rather you can choose a higher gear to reduce engine revs which surely the zf box would do.

The reasoning with a car is different - it's because engine braking provides better control. A train does not need this.

Doctor Fegg · 10 Jan 2019

It's more than that. Coasting with a car is actually less efficient in the age of Electronic Control Units. See https://www.lightfoot.co.uk/news/2018/02/02/bad-technique-coast-driving-downhill/ .

hexagon789 · 10 Jan 2019

squizzler said:
I don’t buy the argument that an absence of coasting in the 6speed transmission will be materially detrimental to fuel economy. Ask a motorist: you should never put your car in neutral to coast. Rather you can choose a higher gear to reduce engine revs which surely the zf box would do.

But trains often coast long-distances at speed, so while it likely isn't a problem on a stopping service where you go power-brake, power-brake on say 100mph runs with long sections between stops it could add up having to stay under power all the time.

A BR training video, forget what it's called, mentioned that on longer runs it's often possible to coast for 50% of the time. Certainly when ScotRail used their 170s on the Edinburgh and Glasgow shuttles, drivers would coast for plenty of the route, accelerating to linespeed, coasting and only on longer sections between stops, reapplying power once a bit of speed was lost.

I imagine the Chiltern mainline with its long 100mph sections must see plenty of coasting on the fast services.

43096 · 10 Jan 2019

Bletchleyite said:
They won't end up homeless, they'll go somewhere either for extra capacity or 15x replacement.

Or additional capacity in Ireland?

Bletchleyite · 10 Jan 2019

Doctor Fegg said:
It's more than that. Coasting with a car is actually less efficient in the age of Electronic Control Units. See https://www.lightfoot.co.uk/news/2018/02/02/bad-technique-coast-driving-downhill/ .

That's true of a car, where coasting down a steep enough hill means the wheels turn the engine and so no fuel is injected rather than a bit if you idle and use the brakes to control the descent (not to mention brake lining used).

It's not true of a train, which doesn't descend anything like the same gradients - and adding that a diesel engine has higher compression and thus greater engine braking than a petrol, and so you would need a *very* steep gradient not to need to inject any fuel. My Land Rover Defender in 5th will decelerate on even a relatively steep long hill like the Woodhead Pass. In 6th it will gain speed very slightly. A petrol car would probably need to be in a much lower gear not to gain speed.

pdq · 10 Jan 2019

I'm sure I've read that some modern twin clutch autos (aka DSG from VW group cars) automatically go into coasting mode in situations where remaining in gear would require power to maintain speed due to the engine braking. This saves fuel as the engine is idling rather than being under power. The gearbox switches back into gear almost instantaneously if power or addional engine braking is required.
Are such gearboxes available for large vehicles or is the technology and mechanics only suitable for cars?

Bletchleyite · 10 Jan 2019

pdq said:
I'm sure I've read that some modern twin clutch autos (aka DSG from VW group cars) automatically go into coasting mode in situations where remaining in gear would require power to maintain speed due to the engine braking. This saves fuel as the engine is idling rather than being under power. The gearbox switches back into gear almost instantaneously if power or addional engine braking is required.
Are such gearboxes available for large vehicles or is the technology and mechanics only suitable for cars?

Realistically, because the gradients are mostly smaller and a large diesel engine would provide a lot of engine braking, a train will always require power to maintain speed if it is in gear. So a freewheel is the best option.

Greybeard33 · 10 Jan 2019

Diesel engines do not inherently provide engine braking, unlike petrol engines. In petrol engines the braking effect is provided by the closed throttle butterfly valve restricting airflow into the engine. Diesel engines do not need a throttle valve. It is incorrect that compression of air in the cylinders provides much braking effect - the energy absorbed in the compression stroke is mostly released in the expansion stroke, like a bouncing spring. Therefore some automotive diesels are equipped with artificial engine braking (e.g. "Jake brake") for safety reasons.

If a DMU engine is kept in gear during coasting, there will be some decelerating effect from friction and pumping losses in the engine, plus the hotel loads on the engine (aircon compressor and alternator). But the engine will consume no fuel at all unless the speed drops sufficiently that the driver needs to reapply a short burst of power. On the other hand, if the transmission allows freewheel coasting, the deceleration rate will be a bit less, but the idling engine is burning fuel all the time to overcome losses and provide the hotel power. If power needs to be reapplied, more fuel is wasted accelerating the engine back up to speed.

I should think that it would depend on the route profile (gradients, speed restrictions, distance between stops etc.) which strategy is more economical, but my guess is that coasting in gear would win overall.

edwin_m · 11 Jan 2019

Greybeard33 said:
I should think that it would depend on the route profile (gradients, speed restrictions, distance between stops etc.) which strategy is more economical, but my guess is that coasting in gear would win overall.

Seeing as trains spend a lot of their time coasting compared to road vehicles, I wonder if extra engine wear is a big factor too (engine turning at high speed when coasting, rather than close to idle speed).

t_star2001uk · 11 Jan 2019

Ive just asked a member of our engineering team about this, he was adamant that this is just a rumour and nothing more...

ForTheLoveOf · 11 Jan 2019

superkev said:
're 170 v 172 comparison looking at a recent Rail express magazines monthly 0 to 60 comparison (good read) 172 103 reached 60mph in just 83 seconds with a 170 taking 114 seconds.
For interest some others 185 (68s); 158 (98s); 180 (83s), 220 fastest non electric (53s ); 345 fastest emu (36s).
May be of Interest.
K

Do we know why the 220s are so much faster than other units? They have the same engine as both the 180 and 185, and yet both of those are a fair amount slower (although they have hydraulic transmissions as opposed to electric motors and generators).

superkev · 11 Jan 2019

ForTheLoveOf said:
Do we know why the 220s are so much faster than other units? They have the same engine as both the 180 and 185, and yet both of those are a fair amount slower (although they have hydraulic transmissions as opposed to electric motors and generators).

Torque converted transmissions are non too efficient at lower speeds until they change up to direct drive or higher rations and geneate a lot of heat.
Doesn't someone propose trying a ZF automated manual box which would have no loses from churning oil (Voith) or dragging multidisc clutches (ZF).
Getting off topic now.
K

HLE · 11 Jan 2019

Or better still stick a clutch and manual gearbox in and let's have some fun.

Bletchleyite · 11 Jan 2019

HLE said:
Or better still stick a clutch and manual gearbox in and let's have some fun.

No clutch, but have you driven a heritage DMU?

Prestige15 · 13 Jan 2019

superkev said:
're 170 v 172 comparison looking at a recent Rail express magazines monthly 0 to 60 comparison (good read) 172 103 reached 60mph in just 83 seconds with a 170 taking 114 seconds.
For interest some others 185 (68s); 158 (98s); 180 (83s), 220 fastest non electric (53s ); 345 fastest emu (36s).
May be of Interest.
K

The timing for the 220 is good but how does it compared to a class 800 in diesel power?

Kneedown · 13 Jan 2019

hexagon789 said:
I had actually thought they had done both hp variants of 158s, need to look at that.

I'm not sure it would significantly improve their acceleration, the 400hp was more for hill-climbing so I think it would simply mean they can maintain speed up steeper gradients than either of the 350hp 158 types.

Indeed. As someone who drives both varieties, there is no noticable difference in acceleration. In actual fact the 400hp versions are slower off the mark as full power is not available until you reach 10mph.

hexagon789 · 13 Jan 2019

Kneedown said:
Indeed. As someone who drives both varieties, there is no noticable difference in acceleration. In actual fact the 400hp versions are slower off the mark as full power is not available until you reach 10mph.

That's interesting, you would've thought the more powerful ones would pull away quicker. Are they any better at hill-climbing though?

ac6000cw · 13 Jan 2019

hexagon789 said:
That's interesting, you would've thought the more powerful ones would pull away quicker.

It's available tractive effort, adhesion and wheelslip control that limits maximum acceleration at very low speeds, not power - that only only becomes a factor at higher speeds, when you get onto the 'power limited' part of a typical tractive effort curve - here is an example curve (for a 4400hp loco) - https://www.railforums.co.uk/thread...acquisition-talks.149967/page-12#post-3436183

hexagon789 · 13 Jan 2019

ac6000cw said:
It's available tractive effort, adhesion and wheelslip control that limits maximum acceleration at very low speeds, not power - that only only becomes a factor at higher speeds, when you get onto the 'power limited' part of a typical tractive effort curve - here is an example curve (for a 4400hp loco) - https://www.railforums.co.uk/thread...acquisition-talks.149967/page-12#post-3436183

I appreciate that, no matter how much power you have poor adhesion is poor adhesion. However, I would still have expected, that is either type of 159 was going to be quicker of the mark than the other, it would've been the 400hp variant - it just surprised me a bit , that's all.

Llama · 13 Jan 2019

Kneedown said:
Indeed. As someone who drives both varieties, there is no noticable difference in acceleration. In actual fact the 400hp versions are slower off the mark as full power is not available until you reach 10mph.

My findings are the same. The 400hp units have an almost identical engine (bigger intercooler) but rev lower (1900rpm max vs 2100rpm on the 350 Cummins units). Full traction power is inhibited until a certain speed is reached when starting away, I always assumed it was when the low--speed relay operated but I will check next time I am on one. I wouldn't normally notice because I don't drive them that aggressively.

edwin_m · 13 Jan 2019

ForTheLoveOf said:
Do we know why the 220s are so much faster than other units? They have the same engine as both the 180 and 185, and yet both of those are a fair amount slower (although they have hydraulic transmissions as opposed to electric motors and generators).

The 180 is also a 125mph unit - are you thinking of 175s?

I would guess the difference is something to do with the engine reaching its maximum speed on the lower speed units. Because (at higher speeds) the engine is geared directly to the wheels this limits how fast the wheels can go. Running them faster would need the ratios changing and this would probably result in poorer performance and fuel consumption at lower speeds, or an extra "gear" could be added but this would cost more. As these units are only intended to go at 100mph there's no point in including features that allow them to go faster.

The 22x units have electric transmission, so the wheels are not directly coupled to the engine at any speed. As long as the engine is providing enough power, the transmission can turn the wheels at any speed within the operating range of the traction motors.

Bletchleyite · 13 Jan 2019

edwin_m said:
The 22x units have electric transmission, so the wheels are not directly coupled to the engine at any speed. As long as the engine is providing enough power, the transmission can turn the wheels at any speed within the operating range of the traction motors.

The key advantage of electric transmission is that the engine can operate at its optimal speed independent of the wheels. Far less in the way of losses than a hydraulic DMU which at low speeds wastes a fair bit of energy heating up transmission fluid.

Downside is that it costs more - hence the Class 150 with hydraulic transmission being built instead of the originally proposed Class 210 with electric.

HLE · 13 Jan 2019

Bletchleyite said:
No clutch, but have you driven a heritage DMU?

Never, I was about 20 years too late!

Bletchleyite · 13 Jan 2019

HLE said:
Never, I was about 20 years too late!

I had a go at Wirksworth on a driver experience day - it's amazing how much I'd picked up from sitting behind the driver on the Marple locals and the Conwy Valley! The vacuum brake was the hardest thing to handle, the gears were quite easy.

The Wensleydale is offering DMU experience days in a few weeks if you fancy a go, at a very good price too. Too busy with work to get a holiday for it sadly!

Billy A · 13 Jan 2019

superkev said:
Torque converted transmissions are non too efficient at lower speeds until they change up to direct drive or higher rations and geneate a lot of heat.
Doesn't someone propose trying a ZF automated manual box which would have no loses from churning oil (Voith) or dragging multidisc clutches (ZF).
Getting off topic now.
K

ZF used to actually make a rail version of the AS-Tronic automated manual (used on trucks and buses) though I think the only buyer was the Danish national rail operator which converted their IC3 DMUs from conventional automatic boxes.

Billy A · 13 Jan 2019

Bletchleyite said:
The key advantage of electric transmission is that the engine can operate at its optimal speed independent of the wheels. Far less in the way of losses than a hydraulic DMU which at low speeds wastes a fair bit of energy heating up transmission fluid.

Downside is that it costs more - hence the Class 150 with hydraulic transmission being built instead of the originally proposed Class 210 with electric.

The other downside of electric drive is that traditionally it wasn't very efficient - there's a reason you don't have it in your car!

Chiltern class 172 - Change to hydraulics transmission?

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