Is it difficult to drive an 80x slowly?

[Egg Centric]

Today was the third time I've been on an IEP being driven artificially slowly* and each time it's been jerky - is this possible to mitigate with driving technique or is it pretty much inevitable? I could fully understand that if there is a "minimum" power setting and you are driving the train up a gradient there may be no option at all but to jerk, so that is what I assume is happening. Be good to have confirmation though. Especially cause it seems that this could be mitigated with a software upgrade.


*Not entirely sure why in this case; the reason given by the train manager was it was to 'inspect the track' but he had previously said the train in front was traveling slowly to 'inspect the track'. And the train before, when we passed it, was the yellow banana. So I'm not sure about how much was track inspection because of protocol for a track circuit failure or something, and how much was literal track inspection. Doesn't really matter I guess.

 

[ComUtoR]

Especially cause it seems that this could be mitigated with a software upgrade.

How ? What would the software be doing ?

I know that 'jerk' can be adjusted but in this case I'm unsure of what was actually happening.

 

[Egg Centric]

How ? What would the software be doing ?

You could permit a very subtle application and release of power (more I think about it, it may be the release of power that gives the greater jerk). I don't know anything about the underlying drivetrain but I'd be amazed if it wasn't possible.

I actually suffer from this issue in my main car which has an electronic throttle so I am sympathetic towards drivers facing this kind of restriction (as I am towards poor sods trying to make rapid gear changes with a clutch delay valve). In my case solvable with a remap. In the case of an IEP, surely solvable with something which allows smoother power application and release - perhaps through software-controlled damping? In principle, an electric motor should be infinitely throttleable...

 

[irish_rail]

This is an issue with most new trains. Especially IETs on electric. I always try to use minimal power notch changes at lower speed, as eveeytime power is shut off there is a noticeable jolt, especially so on electric. It is less of a problem when on a diesel set with an engine out, this always gives for a smoother ride. Some drivers unfortunately don't care and so the jolts become even more noticeable.

 

[Egg Centric]

Just theorising, but could it perhaps be that "they" want a power shut-off to be instant for safety reasons?

Do IETs have notches or infinitely variable throttle?

 

[hexagon789]

Just theorising, but could it perhaps be that "they" want a power shut-off to be instant for safety reasons?

Do IETs have notches or infinitely variable throttle?

The (Traction & Brake Controller) TBC is infinitely variable in traction and braking. There is an initial detente in both traction and braking however - I think minimum power is 10% and minimum brake is 20%?

Perhaps a driver can confirm those figures are correct.

 

[Egg Centric]

The (Traction & Brake Controller) TBC is infinitely variable in traction and braking. There is an initial detente in both traction and braking however - I think minimum power is 10% and minimum brake is 20%?

Perhaps a driver can confirm those figures are correct.

If so, it certainly sounds to me (without any expertise at all) that this is a fully solveable issue if it's something Hitachi "cared about". Just make it so either any commanded throttle release, or alternatively a gentle commanded throttle release from 10% results in a 1 second (0.5?) sigmoid curve(?) release down to 0.

Is there some operational reason a rapid shut off is required?

 

[hexagon789]

Is there some operational reason a rapid shut off is required?

The only thing I can think of is that in an emergency situation, you'd want power cut as near as instantly as possible, on putting the TBC to OFF or beyond into a braking setting.

 

[boiledbeans2]

[...]
I actually suffer from this issue in my main car which has an electronic throttle so I am sympathetic towards drivers facing this kind of restriction (as I am towards poor sods trying to make rapid gear changes with a clutch delay valve). In my case solvable with a remap. [...]

OT:
Yes, modern cars suffer from this. It's a phenomenon known as "rev hang". I counter this by releasing the accelerator a split second before releasing the clutch, where the engine brake will start to pull down the rpms for a split second (or I have successfully tricked the software). With some practice, you will get quick and smooth shifts and you won't feel the engine brake at all.

 

[KT530]

Can mitigate to some extent by holding in minimum power before shutting off power, but yes they are pretty dire at low speed, most notably at 20 mph and below, you certainly feel a small jolt at the front.

As Irish_Rail mentioned above, this is slightly better in Diesel mode.

You may also feel a momentary glide and jolt at around 9 mph under braking too, when the dynamic braking cuts out. Again this is pretty dire for a new train.

Comparatively, a 387 for example can be driven much more smoothly and the dynamic brake to foundation brake blend is not noticeable.

As with everything, some drivers are more agressive than others and some take into account passenger comfort.

 

[Egg Centric]

OT:
Yes, modern cars suffer from this. It's a phenomenon known as "rev hang". I counter this by releasing the accelerator a split second before releasing the clutch, where the engine brake will start to pull down the rpms for a split second (or I have successfully tricked the software). With some practice, you will get quick and smooth shifts and you won't feel the engine brake at all.

(Also OT):

That’s a slightly different phenomenon which I’ve also encountered many times - but not on my car. I describe two issues: firstly the throttle doesn’t really do anywhere between 0 and 10% and additionally there’s a small delay on application. Secondly the clutch delay valve, while not precluding smooth gear changing, precludes *rapid* smooth gear changing because you match the revs, release the clutch pedal… and then the clutch itself takes about a quarter to half a second to fully release.

These are both minor issues in the grand scheme of things, both of which can be worked around, and most drivers wouldn’t even notice - but irritating if you’re obsessive about it like me

 

[boiledbeans2]

(Also OT):

That’s a slightly different phenomenon which I’ve also encountered many times - but not on my car. I describe two issues: firstly the throttle doesn’t really do anywhere between 0 and 10% and additionally there’s a small delay on application. Secondly the clutch delay valve, while not precluding smooth gear changing, precludes *rapid* smooth gear changing because you match the revs, release the clutch pedal… and then the clutch itself takes about a quarter to half a second to fully release.

These are both minor issues in the grand scheme of things, both of which can be worked around, and most drivers wouldn’t even notice - but irritating if you’re obsessive about it like me

Thanks for the clarification. I've just did a search on "clutch delay valve". It seems to be included only on certain makes of cars, so I've not encountered it yet!

Modern manual gearbox cars are becoming more difficult to drive! It's time to get an EV... so you can pretend you're driving a train with one-pedal operation.

 

[O L Leigh]

What follows is based on no personal experience with IETs, so please bear this in mind.

When I drove electric traction I was always told that you shouldn't just shut off power in one movement because it will introduce jolts and isn't very mechanically sympathetic. These could be particularly harsh at low/moderate speeds when a high power notch is being used. As a consequence, I was taught to pause in notch 1/minimum before selecting off to mitigate against this. The reason seems to be that the motors are still pushing and the train accelerating and just cutting the power creates a backlash in the drive gears whereas pausing in notch 1/minimum eases the pressure on the gears because the motors are no longer pushing against them which eliminates backlash and, therefore, jolts. This seems to be less of an issue with diesel-hydraulic and even diesel-electric traction, but you can still get jolts if you go directly from a high notch to off in one move at low/moderate speeds.

At the risk of implying criticism of my colleagues in dark green for the second time this week, I wonder if the jolts that the OP describes are a consequence of HSS drivers not fully appreciating/being told about this aspect of electric traction handling and could be mitigated by a simple change to driving style.

That said, and referencing back to not having any personal experience with IETs, I wonder if the traction itself might be at least partially responsible for the choppy ride. In another thread, a contributor said that the Stadler FLIRTs just want to run away in almost any power setting and need to be driven with speed set in order to get a smooth ride*. I can see that if notch 1/minimum is still causing the train to accelerate at an appreciable rate at low/moderate speeds it may not be possible for the driver to release the pressure against the drive gears no matter how low the power setting used in the cab and that you'll get a jolt no matter what you do. If this is the case, I can see an argument for remapping the power controller to give less at lower notches than may currently be the case. The alternative suggested by the OP of having a programmed slower more gradual release of power is probably less desirable. If the driver moves the controller to off it's because no more power is needed and therefore to have any sort of delay in response from the train is not necessarily going to be ideal.

* May be starting a new thread on this, as it occurred to me at the time I read it that having so much power in low power notches may not be a good thing. In light of this discussion, I can see now this is one potential way in which it's manifesting itself.

 

[Tynwald]

They are very easy to drive at low speeds

 

[irish_rail]

At the risk of implying criticism of my colleagues in dark green for the second time this week, I wonder if the jolts that the OP describes are a consequence of HSS drivers not fully appreciating/being told about this aspect of electric traction handling and could be mitigated by a simple change to driving style.

Ironically to me it seems most HSS drivers are far more sympathetic driving the IETs, remembering that passengers are on an intercity service. It was drummed into us when learning locos and HSTs how important a smooth ride is.
Whereas the west or GWR drivers , they really seem quite often to only use either full power or full brake (ok slight exaggeration!) In other words they drive it much like one drives a sprinter.