'Eco buses'

[102 fan]

Apparently some new buses are more eco friendly by having thier engines reduced from 9 litres to 5. How is the lessened litreage accounted for? Higher gearing?

 

[90019]

Some are hybrids - our single deck Volvo B5s use the electric motor to make up for the lack of torque down the bottom end of the rev range. It's very noticable when the batteries occasinally drain completely, as they are incredibly slow pulling away until the turbo kicks in.

I believe the B5TL demonstrator we have is a twin turbo 5 litre engine, but I don't know much about it. From what other drivers have said, it's not that quick.
Then again, the newer B7s and B9s have massive flat spots in the performance to meet emissions regs, so aren't that great anyway.

 

[102 fan]

I don't believe that 3 litres can be lost without detrimental performance.

 

[mbonwick]

Apparently some new buses are more eco friendly by having thier engines reduced from 9 litres to 5. How is the lessened litreage accounted for? Higher gearing?

Higher compression ratios, bigger turbochargers and higher working temperatures are used to get the engine to produce the same power.
Unfortunately the torque bands become very narrow, so it's a case of getting the gearbox setup properly matched to the engine.

 

[edwin_m]

Higher compression ratios, bigger turbochargers and higher working temperatures are used to get the engine to produce the same power.
Unfortunately the torque bands become very narrow, so it's a case of getting the gearbox setup properly matched to the engine.

Presumably this is also good for hybrids where the engine can be kept running at a constant speed for much of the time.

 

[FOH]

There's an interesting update from TfL just out link

 

[mbonwick]

Presumably this is also good for hybrids where the engine can be kept running at a constant speed for much of the time.

The electric drivelines of series hybrids are indeed good in this respect (engine drives a generator which powers a motor), but parallel hybrids aren't great as there is still a mechanical connection between the engine and wheels.

 

[90019]

Unfortunately the torque bands become very narrow, so it's a case of getting the gearbox setup properly matched to the engine.

Our hybrids use Volvo's I-Shift 12 speed gearbox, which is pretty damn good. Since it block changes, you only go through the gears you need, though you can still rev it pretty high in the lower gears - through the first couple on the flat you can redline it.

The rest of the fleet* are Voith four speed, which are fantastic boxes, but I'm not sure how well they'll cope with the shorter torque bands, as they have fairly long gears (with the overspeed in first, you can hit 25mph on some buses). They do struggle with the newer engines and the flat spots in the rev range to meet the emissions regs though, being noticably slower off the mark and running out of puff sooner.


One thing I will note is that Volvo have superseded the Euro 5 B7RLE with the Euro 6 B8RLE, so not all engines are getting smaller.


*With a few exceptions.

 

[102 fan]

Higher compression ratios, bigger turbochargers and higher working temperatures are used to get the engine to produce the same power.
Unfortunately the torque bands become very narrow, so it's a case of getting the gearbox setup properly matched to the engine.

Does the HP remain the same?

 

[hassaanhc]

The rest of the fleet* are Voith four speed, which are fantastic boxes, but I'm not sure how well they'll cope with the shorter torque bands, as they have fairly long gears (with the overspeed in first, you can hit 25mph on some buses). They do struggle with the newer engines and the flat spots in the rev range to meet the emissions regs though, being noticably slower off the mark and running out of puff sooner.


*With a few exceptions.

I've found the B9TL with a Voith 4 speed gearbox is significantly slower than one with a ZF 6 speed, and seem to have a flat spot in first. I've noticed this on Tower Transit 36136-165 and Metroline VW1301 which are all Voith (Metroline have randomly mixed ZF and Voith buses in the same batch).
London General VE1-3 which are Euro 4 are much quicker off the mark.
With E400s from Euro 5 they've particularly reduced the acceleration of them, however both Voith and ZF have roughly the same performance. Likewise E200s have same performance with the two gearboxes they come in (although the Voith is only 3 speed with them, vs 4 speed Allison).

 

[90019]

I've found the B9TL with a Voith 4 speed gearbox is significantly slower than one with a ZF 6 speed, and seem to have a flat spot in first. I've noticed this on Tower Transit 36136-165 and Metroline VW1301 which are all Voith (Metroline have randomly mixed ZF and Voith buses in the same batch).

The newer ones are definitely slower than the older ones, but there is a little bit of a lag in the B9TLs, which the B7TLs and RLEs don't seem to have so much. They do seem to be faster than the ZF 6 speed boxes once they get going though, especially with the overspeed in first working.

The only experience I have of actually driving buses with ZF 6 speed boxes are two 55 plate B7RLEs which are both utter crap and hated by pretty much every driver - it doesn't help that neither of them are set up properly and one of them has a slightly knackered gearbox that jolts every time it changes. I think they may also be in eco mode.
The equivalent buses with Voith boxes are sluggish off the mark due to the laggy turbo, but are quick once they get going.

 

[Hornet]

Used one of Dublin Bus new Eco Buses on Sunday. What a wierd experience! Bus came to a halt besides us, sounded like it had broken down as the Diesel Engine cut out. Sat down, doors closed then the whine of what sounded like an Electric Motor before the Deisel Engine chimed back in at around 10kph. was a totally surreal experience. Took me back to the old Electric Milk floats of my youth (Neville & Griffin Dairy of Slough). BTW the bus was not in standard DB colours (Blue/Yellow), but a greyish sort of Green. Reg started with 141-D- and was working the 151 Route from East Wall to Foxborough.

 

[mbonwick]

One thing I will note is that Volvo have superseded the Euro 5 B7RLE with the Euro 6 B8RLE, so not all engines are getting smaller.

Yes and no - logically you'd expect the B7RLE to become the B5RLE, however when you remember that it's basically a coach chassis with modified front framing for a low entrance (hence the LE) you see where the logic comes from.

As part of the rationalisation of engines offered, both the D7E and D9B (which powered the B7R and B9R) were replaced with the D8K (B8R). A fairly sensible step, I think you'll agree. As the low floor version of the B7R, the B7RLE became the B8RLE.

The general trend is downwards though; B13R has become B11R, B9TL has become B5TL etc.
Interestingly ADL have stuck with the Cummins ISBe 6.7 litre unit for their E400s despite the change to euro 6.

Does the HP remain the same?

Broadly similar, the new B5TL may even have slightly more horsepower - but that's not much use if the gearbox isn''t matched to its peak torque.

 

[90019]

As part of the rationalisation of engines offered, both the D7E and D9B (which powered the B7R and B9R) were replaced with the D8K (B8R). A fairly sensible step, I think you'll agree. As the low floor version of the B7R, the B7RLE became the B8RLE.

Ah, that makes sense, I hadn't thought about that.

 

[Mikey C]

Downsizing to smaller turbocharged engines is happening to the car industry to, hence the latest Formula 1 spec of 1.5 Turbo hybrid engines to reflect this.

Whether these more stressed small engines last as well is something we will find out in due course...

 

[starrymarkb]

Yes and no - logically you'd expect the B7RLE to become the B5RLE, however when you remember that it's basically a coach chassis with modified front framing for a low entrance (hence the LE) you see where the logic comes from.

As part of the rationalisation of engines offered, both the D7E and D9B (which powered the B7R and B9R) were replaced with the D8K (B8R). A fairly sensible step, I think you'll agree. As the low floor version of the B7R, the B7RLE became the B8RLE.

The general trend is downwards though; B13R has become B11R, B9TL has become B5TL etc.
Interestingly ADL have stuck with the Cummins ISBe 6.7 litre unit for their E400s despite the change to euro 6.


Broadly similar, the new B5TL may even have slightly more horsepower - but that's not much use if the gearbox isn''t matched to its peak torque.

Isn't the new single deck bus chassis the B5L (which isn't sold in the UK because operators don't like full low floor to rear with 'shower cubicle' engine

 

[BuhSnarf]

This is also common in cars where a good ford eco engine of say 1.1l is equivalent to a 1.6 of old. My new 1.5 diesel feels a lot punchier than old 2l diesels I've driven.

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