27 February 2013 | Product | Issue 304
Power delivery
Hybrid technology need not involve the use of an expensive battery pack. Alternative approaches can be considered, most notably the use of a flywheel-based KERS: Kinetic Energy Recovery System.
One should be available in Wrightbus’s StreetLite by 2014 thanks to co-operation between the Northern Ireland bus maker and Flybrid Automotive, Voith, Productiv and Arriva in a project part-funded by the Technology Strategy Board.
KERS technology has already gained considerable acceptance in motor sport. As a consequence it is perhaps not too surprising to see the Williams Formula 1 team promoting its own package to bus builders and operators through Williams Hybrid Power.
“What we’re talking about here is an alternative means of storing and releasing energy that’s a lot lighter than batteries,” explains head of bus systems, Frank Thorpe. “The flywheel weighs no more than 50kg and the system is designed to last the life of the bus.
“As a consequence operators no longer have to worry about how long the battery pack will go on for and how much it will cost to replace,” he adds.
A KERS cannot store energy in the way a battery does. “However because it recuperates energy quickly then deploys it quickly it is ideal for the duty cycle of urban buses because they are stopping and starting all the time,” he says.
Designed for retrofitting as well as for the OE market, the Williams system has been installed in a 2006-vintage Volvo B7TL and tested at MIRA and is about to be fitted to a B9TL. A 15 per cent improvement in fuel economy can definitely be achieved, says Thorpe, but adds that this is a conservative figure.
“We reckon it will be more like 20 per cent to 25 per cent in service,” he observes.
And the installed price?
“From £30,000 to £50,000,” he replies. “The bearings might require replacing once every five years but that’s the only ongoing maintenance commitment and will cost you around £500.”
The Williams package will be in service in London with Go-Ahead this summer, says Thorpe.
Both Williams and Go-Ahead were recognised in the Low Carbon Champions Awards earlier this year along with Wrightbus and Transport for London. The awards are presented by the Low Carbon Vehicle Partnership.
While much of the focus on the application of hybrid technology has, not surprisingly, been on what is happening in London with major orders for the Borismaster, more and more provincial fleets are going the hybrid route. For the moment at least it is diesel-electric technology that is primarily being deployed.
Network Warrington and Ensign Bus are among regional operators who have recently put hybrids on the road.
The latter is operating six Wrightbus-bodied Volvo B5LHs on routes in and around Thurrock in Essex. Although it is early days, engineering director Brian Longley is pleased with their performance so far.
“We had a couple of software glitches but Volvo put them right quickly,” he says. “We’re getting 8.5mpg out of them compared with 6.0 to 6.5mpg from the Volvo B9s we were using previously so we’re looking at a fuel saving of around 35 per cent.”
Clearly that is more than can be achieved through a KERS: but there is of course the cost of eventually replacing the batteries to worry about. Longley however is not too concerned.
Steady improvements in battery technology being achieved in the Far East will improve performance and drive down costs he believes. “Put it this way – because of the fuel saving we’d seriously look at hybrids like this even if the Green Bus Fund which has supported us with this acquisition didn’t exist,” he states.
The Volvos are equipped with a 4.8-litre diesel and a parallel hybrid drive system which allows them to travel silently at low speeds for short distances on battery power alone.
“It’s a bit of a learning curve for the drivers because they can sometimes forget and attempt to re-start the engine, which can cause problems,” Longley says. “We have to impress upon them that there is no need to do so if the big blue light on the dashboard is illuminated.”
He reveals that Ensign is one of the first operators to add hybrid Volvos to its fleet without an accompanying maintenance package.
“Although all our vehicles are of course properly-maintained, it can be a little difficult for us to schedule in planned maintenance with a dealer because we do a lot of rail replacement work,” he says. “This means that vehicles may have to be deployed suddenly and at short notice.”
As a consequence its own technicians have been trained to work on the vehicles and know how to deal with high-voltage systems.
Ensign’s extensive and well-established used bus and coach sales operation means that it can look on the prospect of disposing of hybrids second-hand with equanimity.
Volvo recently announced that from 2014 onwards its complete low-floor city buses would only be offered as hybrids on the European market.
Now available with something called arrive and go, which means the bus relies far less on its diesel engine and far more on its batteries, the series hybrid system produced by BAE Systems can produce fuel savings of anywhere from 25 per cent to 40 per cent contends Ian Wilson, business development director for its HybriDrive operation. He argues that hybrid buses can make financial sense even without government grants if operators are prepared to countenance extended payback periods.
“We’ve recently supplied 102 hybrid systems to Irisbus for buses going into service in Dijon in France,” Wilson says. “It’s a 15-year contract and having looked at the fuel savings the operator is confident that payback will be achieved within that time.”
The vehicles have been acquired without a government subsidy, Wilson adds, but that is not to say that he dismisses the value of initiatives such as the Green Bus Fund: far from it. “Without it the economics of introducing hybrids would have been challenging,” he admits.
By enabling operators to put hybrids into regular service he says it has put to bed any concerns they might have had that such vehicles would not be able to stand up to the pressures of day-to-day operation. “They now believe in the technology,” he states.
Wilson anticipates that the direction in which BAE Systems is developing its hybrid drive will ultimately result in what in effect will be an all-electric bus. With city authorities set to enforce ever-lower emission levels over the next few years, such a vehicle is sure to have wide appeal he believes.
While reticent about the cost of battery replacement, Wilson says that prices are likely to fall long-term.
As for durability, he points out that the batteries HybriDrive employs are warranted for five years and will probably last for from five to eight years. “We have batteries in service in London that are now over four years old and there is no indication of a significant deterioration in performance,” he observes.
Not all transmission manufacturers are eager to market hybrids. ZF says it has a package available, but will not put it into production until it has a volume order.
As its involvement in the Flybrid programme indicates, Voith is rather more enthusiastic. Exhibiting its ElvoDrive serial hybrid drive at last September’s IAA Commercial Vehicle Show in Hanover, Germany, Voith is running trials of its parallel system in Berlin but a lot of its activity in this area is taking place in the USA.
US-based Allison Transmission’s hybrid transmissions are now in service in over 3,500 buses worldwide on routes in over 160 cities.
The company’s H 50 EP parallel package has been installed in five Solaris Urbino 18m artics operating in Oslo. “Depending on the duty cycle and the driver’s skill, fuel consumption can be reduced by around 22 to 24 per cent,” contends Solaris Norway managing director, Terje Bjorndalen.
A similar vehicle operated by Stadtwerke Neuss in Neuss near Dusseldorf in Germany saved 1,750 litres of diesel in just four months.
Turning to conventional transmissions, Voith is forging ahead in the midibus sector and is now supplying automatic boxes to ADL, Wrightbus and Optare.
The last-named manufacturer recently received an order from Stagecoach for 32 SlimLine 9m Solo SRs equipped with four-speed DIWA 824.5 boxes. “The Cummins-Voith driveline is new to Optare and is being fitted at the specific request of Stagecoach,” says Optare commercial director, Chris Wise.
The IAA saw Voith unveil a new package with the imminent arrival of Euro 6 in mind.
It consists of the new four-speed DIWA.6 auto box accompanied by Voith’s SensoTop programme – it changes gear at the optimum points commensurate with the terrain the vehicle is travelling through – and its DIWA SmartNet telemetric system. SmartNet continually monitors the transmission and immediately warns the operator if there are any problems so that they can be addressed the minute the driver returns to the depot.
DIWA.6 is up to five per cent more fuel frugal than its predecessor, claims the manufacturer. Included in that figure is a saving of up to three per cent provided by changes to the operating pressure.
“It automatically adjusts to the output required during the bus’s stop-start cycle and is reduced whenever possible,” says Voith sales and marketing manager, John Domigan.
An optimised Automatic Neutral Switch allows the transmission to stay de-coupled from the engine for longer when the vehicle is stationary, also lowering fuel usage.
Other changes compared with predecessor boxes include modifications to the gear pump, heat exchanger, converter pump, acoustics and housing and preparation for stop-start. The new planetary carrier is lighter – any weight reduction helps offset the weight penalty imposed by Euro 6 as well as cutting fuel usage – but maintains the same strength as that of previous models, says Domigan.
Further fuel savings are provided by an intelligent start-up management system.
“Sensors detect if the bus is rolling backwards during starting and ensure that it stays in neutral for as long as possible,” he says. “The result is that the engine doesn’t have to work against the active brake, and burn fuel unnecessarily.”
