Welsh Class 158 transmission

[hexagon789]

It is fully automatic in a 195 yes, there's no provision for the driver to have any input into gearing, however the 195s have four 'powerpack' modes that the driver can select - 'eco', 'normal', 'power' and 'super power'. These change the speeds at which the gearbox changes up - in eco the gearbox changes up at lower revs, in super power mode the gearbox makes more use of the rev range of the engine. The two intermediate settings are somewhere in between.

Guess which powerpack setting most 195s are found to be in when relieving another driver on a journey...

Why four different modes though? Wouldn't two be enough?

 

[Llama]

Why four different modes though? Wouldn't two be enough?

Yep, I've never used the two middle settings other than to check what they do.

 

[hexagon789]

Yep, I've never used the two middle settings other than to check what they do.

And the only difference is that each "mode" progressively shortens the change-up speed? There's no engine up-rating?

 

[Llama]

Yes that's right, 522 flywheel hp is on tap in each setting we are told, the difference is all in the gearbox operation, and that seems right from my experience driving them.

 

[ic31420]

How does the eco mode work on the 185s?


(Mods are going to be having a thread drift red pen meltdown on this one - something that spoils this form imho)

 

[Bletchleyite]

How does the eco mode work on the 185s?

By knocking out the engine in one coach (which rotates to ensure engine hours and therefore overhaul schedules are the same) - a completely different concept.

 

[Llama]

That's a concept that's not possible on the 195s, due to the design of the gearbox which isn't self-lubricating when the engine attached to it isn't running. The economies of some mechanical transmissions vs hydrodynamic transmissions aren't as simple as first meets the eye.

 

[ic31420]

By knocking out the engine in one coach (which rotates to ensure engine hours and therefore overhaul schedules are the same) - a completely different concept.

Quite blunt then!

I've been doing some digging and it seems the drivers were taught enconomical driving techniques rather than anything being programmed in.

 

[Billy A]

That's a concept that's not possible on the 195s, due to the design of the gearbox which isn't self-lubricating when the engine attached to it isn't running. The economies of some mechanical transmissions vs hydrodynamic transmissions aren't as simple as first meets the eye.

No, they're not. In isolation "mechanical" gearboxes are more efficient because they transmit power mechanically when they lock their torque converters but unless they can provide a coasting facility much of the gains are lost by having to drive the train downhill. ZF make two manifestations of their bus-derived six speeder. The newer one is specifically designed to freewheel and allow the train to be towed if necessary but the downside seems to be jerks when the drive is taken up again.
Seems that Voith actually knew what they were doing when they designed purely hydraulic transmissions all those years ago. No friction materials to wear out, easy coasting and smooth changes.

 

[Bletchleyite]

unless they can provide a coasting facility much of the gains are lost by having to drive the train downhill

Is that actually true? On a modern car engine (with an ECU), the engine uses no fuel whatsoever on the overrun (you get a small jolt when the fuel system kicks back in if you push the accelerator) though you do get some engine braking. Whereas if you coast, a small amount of fuel is used to idle. Is a train not the same?

 

[hexagon789]

Is that actually true? On a modern car engine (with an ECU), the engine uses no fuel whatsoever on the overrun (you get a small jolt when the fuel system kicks back in if you push the accelerator) though you do get some engine braking. Whereas if you coast, a small amount of fuel is used to idle. Is a train not the same?

As the engine is still idling surely fuel is still consumed while running with the power off with a mechanical gearbox? The advatange of the Voith hydraulic over the ZF being that you can coast at speed for some distance whereas with the mechanical you need to use power more often to hold speed and that includes downhill?

 

[Bletchleyite]

If you coast, power is used. If you are on the overrun i.e. in gear with engine braking, no power is used, the ECU will turn the fuel off entirely as the movement of the wheels turns the engine.

 

[Billy A]

Is that actually true? On a modern car engine (with an ECU), the engine uses no fuel whatsoever on the overrun (you get a small jolt when the fuel system kicks back in if you push the accelerator) though you do get some engine braking. Whereas if you coast, a small amount of fuel is used to idle. Is a train not the same?

The issue is that without a coasting ability you'll have engine braking so the train will tend to slow down going downhill so the driver will have to take power - and diesel - to maintain speed. With a hydraulic transmission the train can coast for quite long distances, admittedly using some fuel while doing so as the engines will be ticking over.. There's swings and roundabouts about it but I understand that user experience is that the fuel savings with the non-coasting ZF gearboxes weren't as good as expected.

 

[hexagon789]

If you coast, power is used. If you are on the overrun i.e. in gear with engine braking, no power is used, the ECU will turn the fuel off entirely as the movement of the wheels turns the engine.

But surely the engine is still running, so still using fuel?

 

[Bletchleyite]

But surely the engine is still running, so still using fuel?

No, because the road wheels are turning it so the ECU shuts the fuel off. If revs start to drop (e.g. the driver presses the clutch) the fuel starts being injected once more.

 

[edwin_m]

But surely the engine is still running, so still using fuel?

A post above mentions that the extra fuel used because the driver needs to apply power downhill to keep the speed up has been found is more than what is saved by not having to keep the engine turning when it is disconnected from the wheels. The dynamics of a train are different from a car, which encounters much steeper gradients but also has much more rolling resistance for other reasons (tyres). So the effect of leaving a car engine clutched in when coasting is much less noticeable than with a train.

 

[37057]

By knocking out the engine in one coach (which rotates to ensure engine hours and therefore overhaul schedules are the same) - a completely different concept.

To add to this, the shut down is initiated automatically by either speed set or GPS coordinates. Also manually via TMS when at a stand still.

 

[Llama]

Is that actually true? On a modern car engine (with an ECU), the engine uses no fuel whatsoever on the overrun (you get a small jolt when the fuel system kicks back in if you push the accelerator) though you do get some engine braking. Whereas if you coast, a small amount of fuel is used to idle. Is a train not the same?

Yes, 195s need a slight amount of traction power applied in order to keep at a certain speed on all but the very steepest falling gradients where say a 150 or 185 would coast freely maintaining speed.

 

[hexagon789]

No, because the road wheels are turning it so the ECU shuts the fuel off. If revs start to drop (e.g. the driver presses the clutch) the fuel starts being injected once more.

So the engine is kept turning over by the wheels and not by fuel then?

 

[hexagon789]

A post above mentions that the extra fuel used because the driver needs to apply power downhill to keep the speed up has been found is more than what is saved by not having to keep the engine turning when it is disconnected from the wheels. The dynamics of a train are different from a car, which encounters much steeper gradients but also has much more rolling resistance for other reasons (tyres). So the effect of leaving a car engine clutched in when coasting is much less noticeable than with a train.

I think I understand now, that's explained nicely cheers

 

[Bletchleyite]

So the engine is kept turning over by the wheels and not by fuel then?

Yes. Only happens on a modern car with fuel injection and ECU though. On a traditional car with a carb etc it would continue to burn fuel.

Alongside the benefits of engine braking it's another reason not to coast in neutral when stopping a car but instead to stay in gear until the point you'd stall otherwise.

 

[hexagon789]

Yes. Only happens on a modern car with fuel injection and ECU though. On a traditional car with a carb etc it would continue to burn fuel.

Alongside the benefits of engine braking it's another reason not to coast in neutral when stopping a car but instead to stay in gear until the point you'd stall otherwise.

Apologies, I was actually meaning Class 195s (!), but Edwin explained it very well so it doesn't matter.