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Post by ted672 on Jun 5, 2018 11:58:55 GMT
With the early stages of ATO being introduced on the Sub Surface Railway, I was wondering whether the system employed allows trains to coast. My experience on the Central line is that trains are either under power or braking, which can result in an uncomfortable ride at times. There are some sections on the District line between Elm Park and West Ham where coasting is a regular event under manual driving and I was wondering if the comfort of the journey would be adversely affected by the change to ATO?
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class411
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Post by class411 on Jun 5, 2018 12:07:51 GMT
Coasting when using electric power is not the same as coasting in something driven by an internal combustion engine. Apart from friction (ignoring regenerative breaking), the electric motors do not provide 'engine breaking' as an IC engine does.
It's a pretty safe bet that modern control systems are capable of very fine granularity in the amount of power delivered, so they can probably deliver just enough to overcome the various drag factors on the train - friction and wind resistance. But there is no reason why a ATO system should not deliver zero power if, for example, the train is gently descending at a constant speed. There are no adverse safety considerations to it behaving in that way.
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Post by brigham on Jun 5, 2018 12:08:26 GMT
Or the running costs, for that matter.
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Deleted
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Post by Deleted on Jun 5, 2018 12:14:05 GMT
Thales TBTC currently on the northern and jubilee is very harsh at times either full motors or full brakes most of the time.
Thales CBTC is apparently promised to deliver a smoother ride but it’s only as good as the person or persons that programme the software. I’m sure though once it’s live there will be constant adjustments made
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North End
Beneath Newington Causeway
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Post by North End on Jun 5, 2018 12:29:01 GMT
Thales TBTC currently on the northern and jubilee is very harsh at times either full motors or full brakes most of the time. Thales CBTC is apparently promised to deliver a smoother ride but it’s only as good as the person or persons that programme the software. I’m sure though once it’s live there will be constant adjustments made The trouble with Seltrac is the system simply selects a speed and then sticks to it. It’s a myth that it doesn’t coast, as it does, just that sooner or later an adjustment will be made to get back close to the desired speed. More daftly, when regulating itself it selects a “velocity ceiling”, so for example Warren Street to Goodge Street if running early the train may become limited to 20mph. Even on the steep downhill gradient it will brake to ensure this is not exceeded. Then a wheelchair gets on and all of a sudden the train is late! The Vic Line is much better, it will determine a coasting point after leaving a station if running early. This is much better all round. LU have looked at modifying Seltrac to do this - and surprisingly enough it’s too expensive relative to the benefits. One would have thought LU might have learned their lesson after being lumbered with an off-the-shelf system bequeathed by Tube Lines. Unfortunately the two changes of mind with the SSR resignalling has left them in a highly unfortunate and weak position - and this will be felt especially when the time comes to pay for the next round of resignalling. |
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Deleted
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Post by Deleted on Jun 5, 2018 12:49:22 GMT
From my daily experience of the Jubilee, the current signalling improved massively since the introduction - right after the switchover it was common to have rapid jerky switching of speed: a tiny bit up, a tiny bit down, instead of coasting. But nowadays it is clearly able of sustaining at least some coasting.
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Post by ted672 on Jun 5, 2018 15:09:20 GMT
Thanks for the responses. I did wonder if the system was capable of "zero power" and/or "zero brake". It will be interesting to travel on the line when it's part manual and part ATO.
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Post by bigvern on Jun 5, 2018 17:05:51 GMT
When the Thales TBTC was being developed it had to meet headway targets set by LUL and computer modeling was used to maximise headways, trains however were kept to 0.5 mph of the Target speed as a result train would be constantly motoring on and off on uphill gradient and braking on downhill gradient, this did mean a more jerky journey, in addition the trains traction software was set to a maximum rate, rather than at 50% when interrunning with the old trains and signalling system as overlaps would be compromised. over time tweaks to the system have been made to smooth things out, although we may have just become 'used'to the new train performance under TBTC.
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class411
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Post by class411 on Jun 5, 2018 17:34:29 GMT
When the Thales TBTC was being developed it had to meet headway targets set by LUL and computer modeling was used to maximise headways, trains however were kept to 0.5 mph of the Target speed as a result train would be constantly motoring on and off on uphill gradient and braking on downhill gradient, this did mean a more jerky journey, in addition the trains traction software was set to a maximum rate, rather than at 50% when interrunning with the old trains and signalling system as overlaps would be compromised. over time tweaks to the system have been made to smooth things out, although we may have just become 'used'to the new train performance under TBTC. 0.5 mph seems a very low hysteresis, but, if the accelerative and decelerative forces can be controlled sufficiently finely there is no reason why a train cannot proceed smoothly with that value. Does anyone know just how fine a control of traction and breaking force are available to modern ATO systems? |
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Deleted
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Post by Deleted on Jun 5, 2018 17:44:26 GMT
When the Thales TBTC was being developed it had to meet headway targets set by LUL and computer modeling was used to maximise headways, trains however were kept to 0.5 mph of the Target speed as a result train would be constantly motoring on and off on uphill gradient and braking on downhill gradient, this did mean a more jerky journey, in addition the trains traction software was set to a maximum rate, rather than at 50% when interrunning with the old trains and signalling system as overlaps would be compromised. over time tweaks to the system have been made to smooth things out, although we may have just become 'used'to the new train performance under TBTC. 0.5 mph seems a very low hysteresis, but, if the accelerative and decelerative forces can be controlled sufficiently finely there is no reason why a train cannot proceed smoothly with that value. Does anyone know just how fine a control of traction and breaking force are available to modern ATO systems?
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Post by t697 on Jun 5, 2018 17:52:55 GMT
Does anyone know just how fine a control of traction and breaking force are available to modern ATO systems? And one could ask the same question about the SSR system...  Oh how cruel. |
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class411
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Post by class411 on Jun 5, 2018 18:29:11 GMT
And one could ask the same question about the SSR system... Oh how cruel. I see what you did there.  |
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Post by banana99 on Jun 5, 2018 20:34:21 GMT
As a daily user of the Jubilee Line it is perfectly fine if the timetable runs its course. However if one if following closely another train it can still be very jerky.
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Post by superteacher on Jun 5, 2018 22:02:27 GMT
The Central line ATO does have a coasting option, but I’ve no idea if it’s ever used in practice.
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Deleted
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Post by Deleted on Jul 5, 2018 14:16:59 GMT
I read somewhere that the coasting on the central line needs to be turned on by the line control room.
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North End
Beneath Newington Causeway
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Post by North End on Jul 5, 2018 14:22:37 GMT
I read somewhere that the coasting on the central line needs to be turned on by the line control room. Others may correct, however I have a feeling the coasting function on the Central has never been used. |
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Tom
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Post by Tom on Jul 5, 2018 21:14:06 GMT
North End is correct, coasting vectors appear in the ATO data but are commented out so that they don't apply.
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