Pushing the frontiers of electric power

first_imgFor nearly two decades Wrightbus has been at the forefront of electric bus technology. With a range of products under its belt, it has now unveiled the next generation about to go into production. Mel Holley reports from Northern IrelandBased on the StreetLite EV, the new StreetAir WF comes in 8.8 and 9.5m versionsIt was in 1998 that Wrightbus started work on its long-established ElectroCity brand. Its hybrid and electric development has been relentlessly driven by founder William Wright who, despite his 88 years, remains as sharp and up-to-date as ever. “Back then we were a lone voice in the wilderness as fare as pure electric battery buses were concerned,” he says.In 2002 its prototype single-decker battery-electric plug-ins used the best technology available. But while 30 miles on lead-acid batteries wasn’t going to hit the spot, demonstrations proved that a modern low-floor electric bus powered is the future. And it still is.Todays’ cutting-edge technology is a world away from what was available then and with 1,000 hybrids in service in London, Wrightbus has gained a wealth of knowledge and experience about the vital aspects of battery chemistry and the vital battery management systems (BMS).ChallengeThe challenge thrown down by London and Paris for large numbers of pure-electric buses has concentrated manufacturers’ minds. Says Wright Group CEO Mark Nodder: “We’ve never been frightened of taking on a challenge.”Welcoming the £30m Office for Low Emission (OLEV) announcement for 326 low-emission buses and infrastructure (routeONE News, 27 July) he says that while orders have yet to be placed, the firm is “actively engaged with customers.”The goal is clear, he says: “We all have a challenge of making this technology affordable, viable and operating without compromise.” He acknowledges that without the support of the Green Bus Funds and OLEV, we wouldn’t have the current quantity of electric and hybrid buses on the road.Launching its next generation – the StreetAir name will apply to all Wrightbus low-carbon vehicles – Mr Nodder says a battery-electric double-decker will follow along with a “new project” to be revealed later in the year.Adds Electric Vehicles Head of Product Development Jim Morrison: “Technology never stands still,” adding that this next generation of products will continue to evolve as fast as the technology allows.Two new busesWrightbus has taken its existing StreetLite EV design – the successful battery-electric running in Milton Keynes – as the basis for its StreetAir EV at 8.8m and 9.5m. In ‘wheel-forward’ form (door behind the front axle) the eight buses in Milton Keynes have clocked up 800,000 miles.The revised version’s range is 130-150 miles, depending on the route characteristics, with a maximum single-door capacity of 54.Its bigger brother – and the key subject of the launch – is the single-decker StreetAir EV at 10.6m. If it looks slightly familiar, that’s because it is.It uses Wrightbus’ StreetDeck integral diesel-double decker chassis, married to the strengthened roof section used on Wrightbus’ single-decker hydrogen fuel-cell vehicles. This is required to carry the 1.5T of batteries.Available in single or two-doors, the latter has capacity for 72 passengers with a 150-180 range.A heavier future?Ultimately, the larger StreetAir could go to 12m, but only if weight limits are increased to 19T. Says Sales MD Ian Downie: “We will only build products that comply with existing legislation and that is what we have to work within.”However, BYD has obtained an exemption in London for its pre-production prototypes. This is not a route Wrightbus will pursue. But, says William Wright “Not having this limit puts us at a disadvantage against manufacturers from other parts of the world that already have 19T, such as China. We could easily go to 12m and we are calling for the government to make the change.”Battery technologyWrightbus is offering two battery chemistry and three charging options.Lithium Nickel Manganese Cobalt (NMC), with double the life cycle of a phosphate battery, is suitable for overnight charging and distance driving. It works best with overnight battery balancing and is offered for plug-in buses.Lithium Titanium Oxide (LTO) is suitable for rapid charge, such as hybrids or opportunity charging – it can cope with many more charge/discharge cycles – and needs less frequent battery balancing.The 2.5 years experience in Milton Keynes with NMC has proved that 17 hours service or 135 miles daily, with 12 minute opportunity charging, is achievable day-in, day-out.This uses inductive power transfer (IPT) – the contactless system using charging coils in the road at stops. The alternative is conductive charging using a drop-down pantograph onto charging rails on the bus’ roof, taking around seven minutes.It’s easy to buy batteries and electric motors and create an electric bus, but without a sophisticated BMS, it won’t work very well.All new 10.6m StreetAir battery-electric use StreetDeck chassis and Eclipse 3-style roofWrightbus has Active BMS under development. Based in the Cloud it is accessible anywhere via the web and shows a range of telematics. Aside from GPS and the route travelled, it shows battery condition, state of charge, current and past faults, and can provide alarms if there’s a problem.Remote live diagnostics is increasingly the way that engineering teams will track, monitor and plan maintenance for their fleets.Choices, choices…Another innovation is the development of zero-emissions heating systems, to avoid using a diesel-fired heater. One, a heat-pump is fitted to the two-door development vehicle, shortly to go to London for in-service trials. The other system has yet to be revealed. “We’re pushing the frontiers with technology here,” says ElectroCity Project Manager Robert Brayshaw.Other development is on a revised driveline. Currently a Siemens motor replaces the gearbox in a conventional driveline. An in-line motor arrangement is under development.In short the choices are different lengths (and hence passenger capacities), three types of charging and two types of battery. Wrightbus will recommend the best for each set of operating circumstances.On the roadA short test drive around a go-kart circuit revealed that both buses drive and ride very well. The StreetLite underpinnings of the 8.8m version retain the diesel cousin’s good road manners, along with precise steering and handling. Being smaller and lighter, it’s slightly quicker off the mark. Internally the Dana rear axle is quiet; this is offset by a gentle electrical ‘hum’ that doesn’t change in pitch or tone whether stationary or moving.While the weight on the roof isn’t noticeable, under hard cornering (not of the type you’d expect in normal bus use) there is some body roll. The test bus, which has been as far afield as Switzerland, has 6,500 miles on the clock.For both vehicles, an absence of noise and vibration that diesel drivelines mask means that other sounds become noticeable.At 65dBA, the 10.6m StreetDeck-derived version is 2dBA louder, but that’s mainly down to the noise from the ZF axles/final drive, which will be resolved shortly with some minor tweaks.It’s a pre-production development bus, but there was no electrical ‘hum’ and with the exception of occasional body creak, it’s very tight on normal roads as proved on the 20 mile road section.The interior is to TfL specification, and the rear’s DNA is clearly shared with StreetDeck, but with the attractive ‘barrelled’ roof of the single-decker Eclipse. The weight on the roof is not noticeable, either as a driver or passenger, despite being driven hard around the go-kart track.The regenerative braking on the 8.8m version is perfectly balanced for normal bus work, meaning the service brakes rarely need application. The regeneration software is still being refined on the 10.6m version, and it drives like a diesel bus, with more use of the brakes required.routeONE CommentThe experience that Wrightbus has gained clearly shines through in both StreetAir variants. With OLEV funding neatly meeting its production plans, we’d expect to see them on the streets next year. And we look forward to the EV ‘decker.Make no mistake, this is not the end of the story as Wrightbus’ continuous improvement is running at the same fast pace as battery technology. Not does the UK already have the largest battery-bus fleet in Europe, but it will also remain the most modern.last_img read more

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