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20th September 2009 19:02 |
From Bus and Coach 21st November 2006.
Quote:
Hybrids are coming – from Wrightbus, Volvo, Optare and Alexander Dennis. Growing environmental concerns are fuelling interest in the technology, and in London there’s the political will to make it happen.
The technology has developed slowly. The first venture into hybrids by Wrightbus used a turbine instead of a diesel engine. This proved to be expensive and heavy on fuel. Earlier this year six Wrightbus diesel-electric hybrids entered service in London, initially with mixed results. The fuel tanks were too small, so vehicles ran out of fuel. Drivers forgot to check engine oil levels so engines seized. The buses overheated and had to be fitted with bigger radiators.
Yet, in fairness to all involved, these are simple things – and, as bus manufacturers are well aware, there’s no substitute for real-life operation to show what works and what doesn’t.
But more important than these teething problems is how the buses fitted in to the operation at Go-Ahead London. "We got the impression that the hybrids were considered by some garage staff as nothing more than a nuisance," says one highly-placed insider. "But that all changed when Ken [Livingstone] made his statement on hybrids. Now there’s a real will to make them work."
Other recent trials of hybrids in the UK have not been a roaring success. The Eneco hybrids based on Optare Solos reputedly spent more time off the road than on. But that doesn’t damn the technology, just its application.
The big benefit in running hybrids is reduced pollution. That is driving developments here, and in North America where hybrids are becoming increasingly common. There is also a reduction in fuel consumption. But the big problem is that hybrids are expensive.
"If you’re asking price you’re asking the wrong question," suggests Optare managing director Bob Coombes. "This is about the environment."
The extra capital cost may be recouped by lower fuel costs over the vehicle’s life – but it is a brave operator who justifies investing extra cash up front on a hybrid in the expectation that this will be balanced by smaller fuel bills. And it would be wrong to become fixated on fuel costs. It’s an important cost element, but there are a whole host of other costs to be considered in running a hybrid – and not necessarily all negative. Engines, for example, should last longer, the Wrightbus experience in London notwithstanding.
At the present stage of development hybrids are only going to appear where someone else is willing to foot the bill. And that isn’t unreasonable when the benefits of the technology are for society as a whole, not just for bus users.
There are in fact two technologies – what are described as series and parallel hybrid drives. In a parallel drive the vehicle has two power sources - a diesel engine and an electric motor/battery pack. These are connected to the gearbox in parallel, so that the power to drive the vehicle can be derived from both sources at once. A control system calculates the best blend of power for any given road conditions, road speed and load.
This is the system being used by Volvo. An Integrated Starter Alternator Motor (ISAM) is located between the diesel engine and the gearbox. This acts as the electric motor for power, can start the diesel engine using power from the battery and also operate as a generator to recharge the batteries.
The engine is the new Volvo D5E – a 210bhp four-cylinder, 5-litre unit, and this is linked not to an automatic gearbox, as you might expect, but to the automated 12-speed Volvo I-Shift. Volvo says this provides a broader range of gears and makes it easier to keep the engine running in the optimum speed range for low emissions and good economy.
On a prototype single-decker which is to enter trial service in Stockholm, the battery pack is mounted on the roof. On six double-deckers to be built for Arriva London the batteries will probably be located around the front wheels. The bus uses Nickel-Metal-Hydride batteries. The size and weight of the battery pack depends in part on how far the bus is expected to run on battery power alone. The pack on Volvo’s single-deck prototype weighs 350kg. Battery pack life is forecast to be around five years, which supporters of parallel hybrids say is longer than will be achieved on a series hybrid.
Optare, too, is going for parallel drive using a system provided by GM Allison. This has been proven in North America, where it is in use in over 500 buses. Optare is making it available in the Tempo from late 2007. The GM Allison hybrid drive will be linked to a 250bhp six-cylinder Cummins ISB engine.
Initially Alexander Dennis is developing a series hybrid, the Ecoturas. In a series hybrid the diesel engine is not connected directly to the drive train but instead drives a generator that provides power to the battery or to the electric motor. The electric motor then drives the bus.
Alexander Dennis is working with Magnetic Systems Technology, which has not previously been involved in buses but has produced hybrids for military applications. MST is part-owned by Rolls-Royce, and MST and Alexander Dennis will jointly develop hybrid systems for single and double deck buses, with the units being manufactured by Rolls-Royce Distributed Generation Systems at Winsford in Cheshire.
Prototypes of the Ecoturas will be ready for field trials in 12 months’ time, with production starting in the spring of 2008. However while it is backing a series hybrid for the UK, Alexander Dennis says it will shortly be announcing a separate initiative using parallel hybrid technology for certain export markets.
Alexander Dennis chief executive Jim Hastie stresses that his company is aiming for affordability in its hybrid solutions. "Intervention funding will work in the short-term, enabling small-batch, political purchases but it is not the long-term answer. We need alternative technologies that can pave the way for sensible pricing, even if there is a sensible, initial premium. I believe we are on the brink of that breakthrough."
Wrightbus uses a Siemens hybrid drive train, and its new double-decker, shortly to enter service with Arriva London, is the start of a new hybrid range. Next is a hybrid version of the StreetCar, for operation in Las Vegas. The Wrightbus hybrid has a 1.9-litre diesel engine and uses Lithium Ion batteries.
Wrightbus, too, stresses the importance of commercially-viable hybrid buses. Speaking about the new double-decker, the company’s hybrid vehicles director, Jonathan Poynton, says: "We will be evaluating the results closely in conjunction with Transport for London, but we are confident that the trial will give further credence to the belief that this kind of hybrid technology is a viable alternative to diesel, especially as the vehicles have the range of a conventional bus and can operate from existing depots, without the need for additional infrastructure."
Some engineers will shudder at yet more complexity in their workshops. Hybrids will initially be concentrated in London, but as volumes rise and prices drop, there are bound to be more urban authorities willing to help fund hybrids in their areas.
This could come about as a response to the introduction of Air Quality Management Areas by local authorities. These have been introduced by almost 200 authorities in the UK, and are required where there is the likelihood that air quality will not meet targets set by the government. Most – but by no means all – are in urban areas. Road traffic emissions are the main cause of pollution in those areas where action is needed.
And there’s the North American experience, where significant numbers of hybrid buses are in operation in major cities – DaimlerChrysler alone has almost 1,500 in service or on order which use a series hybrid drive from BAE Systems. The GM Allison parallel hybrid system – being adopted by Optare - is in use in over 500 New Flyer buses.
It’s hard to see hybrids supplanting ever-cleaner diesels, but in areas which are particularly sensitive to emissions the hybrid looks like being the vehicle of the future.
Until, of course, the fuel cell arrives.
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From:- http://www.busandcoach.com/featureStory.aspx?id=1097 |
