Next stop, hybrids08 June 2010

LCVs might be leading the way in terms of hybrid technology, but bus and coach operators are anticipating growing numbers of alternatives to conventionally-powered vehicles, reports John Challen

The Stern report, published in 2006, warned of a 'serious economic downturn unless prompt action was taken to reduce greenhouse gases'. Time will tell whether the recent recession could have been ameliorated if society had acted sooner on combating that particular problem, but the then-Prime Minister Tony Blair saw enough to warrant calling the document 'the most important report on the future I have received since becoming Prime Minister'.

Four years later and the response from the transport sector has been remarkably proactive. LCVs are trialling various technologies to lessen the impact of greenhouse gases, and the bus and coach sector, too, is looking for innovative solutions. Figure 1 shows a snapshot of where the industry currently stands with regards to available alternative fuels and technologies to deliver lower carbon vehicles.

So what's happening? One of the biggest deals is London's ambitious plan for hybridising its bus fleet. Of the 56 hybrid units currently running in the UK's capital (see case study on pXX), 17 have been provided by Alexander Dennis. ADL hybrids programme manager Andrew Boulton is monitoring their progress carefully, and comments that, so far, there have been advantages and disadvantages.

"In a series hybrid, the diesel engine is decoupled from the road wheels and can operate independently of speed. It can run in its most efficient operating range and is not subject to the rapid rpm changes that are prevalent in normal bus operations," he observes. Such a scenario allows the bus to achieve better fuel consumption, as well as reducing NOx and particulates emissions – again a benefit of rpm being held within the engine's sweet spot.

"As the final drive is electric, there is no gearbox and, as such, no gear changing, so the drive is smooth and stepless," continues Boulton. "Also, since the engine tends to be operating in a narrow operating band, the unit tends to be quieter than the traditional diesel version."

However, Boulton believes bus operators shouldn't get too carried away just yet. "The weight of the battery, motor and generator are greater than the weight of the gearbox they replace," he warns. "Hybrid technology in the UK is also relatively new, and with all trial vehicles currently at an early stage of development, there will undoubtedly be some early life issues as manufactures ramp up the learning curve."

Additionally, there are concerns about safety. While not stirring the same fear as hydrogen-fuelled transportation, the high voltage levels in bus depot environments leave some people worried about hybrids' maintenance. "The systems themselves are inherently safe, but there are perceived concerns with high voltage safety," concedes Boulton. "As a result, there is a further training requirement for operators."

Meanwhile, on the subject of power and range, key to getting hybrids right, he says, is to maximise brake energy recovery and, for this reason, the battery on ADL's hybrids has been selected for its ability to accept power. "The vehicle is configured so that it will start regenerative braking as soon as the throttle pedal has been released," explains Boulton. "In addition, the first inch or so of movement on the brake pedal is only for activation of regenerative braking. As such, the driver has the ability to control the vehicle without having to rely on the foundation brakes. Regenerative braking can slow the vehicle to a full stop."
Beyond that, the ADL hybrid is designed to be load following: it almost operates as a diesel-electric, with the batteries really only used to collect regenerative braking energy and to supply power to the vehicle in pulling away. Hence, the battery charge swing is well managed, which results in a long service life – another key to success.

Options open at Optare
What about Optare? Development work on its Eco Drive hybrids is based on two technologies: a diesel-electric platform, from two well-established companies, and a new mechanical technology. And with 10 of its Tempo low-floor, heavy-duty, single-deck hybrid models now in service in London, Optare reckons it is gaining valuable real-world experience in diesel-electric hybrid technology.

Tempos use the Allison EP40 system, of which over 1,000 are now in service around the world. The main power unit is the Cummins 250hp ISBE Euro 5 engine, and the system incorporates a dual power inverter. Six Panasonic nickel metal hydride batteries, as used in the Toyota Prius, are installed and can be replaced on a fixed price basis. Interestingly, EP40 also comes with a two-year warranty, extendable to five years.

Both the Optare Versa and Solo lightweight, low-floor models will be available shortly with the Siemens series hybrid drive, matched to the Mercedes-Benz OM904La Euro 5 engine. This system uses two drive motors, with a combined gearbox and a single generator, as in the Mercedes-Benz Cito. ISE super capacitor energy storage is employed and the electrical system and engine cooling unit are roof-mounted.

Meanwhile, as also reported in January's Transport Engineer, Optare is one of the partners in Flybus, a project that will investigate the application of mechanical hybrid technology to both new build vehicles and, critically for a lot of operators, also retrofits. Principal benefits expected from this mechanical system are a predicted halving of the weight compared with existing hybrids, as well as the space requirements and the price.

How much for a hybrid?
It is clear that initial costs for all hybrid products are above those of standard diesel vehicles. For the field trial vehicles we're talking about 65% extra for a double decker and 85% for a single decker. Over time, however, everyone expects demand and volumes to reduce costs – although maybe not dramatically.

That said, the issue is to assess the economics of hybrid bus operation and also to calculate the effects of emission reduction – and for this, fleet managers need to look at whole life cost of the vehicle. Let's look at ADL's example of an Enviro400 hybrid compared against the cost performance of a Euro 4 and Euro 3 diesel vehicle.

If we assume that most of the subsystems remain the same, the only aspects likely to change cost of ownership are the engine, gearbox, motor, generator, battery, PCS and brakes. In this example, the engine is downsized from the six-cylinder ISBe and also its duty cycle will be lighter – meaning a longer life and longer oil drain interval.

Also, the hybrid vehicles are not fitted with automatic gearboxes, but do have a motor, generator, battery and PCS. Then again, the braking system of a hybrid is more lightly used, owing to the more efficient operation of regenerative braking compared with conventional retarders.

ADL allows comparison by providing a spreadsheet that calculates the difference in cost of ownership by assessing the annual cost of operating and maintaining a conventional the vehicle, based on fuel oil and adblue, compared with that of a hybrid, including the cost of maintaining the transmission, hybrid system and batteries. Assumptions on unit life are all changeable, to allow for operators' experience and perceptions.

Operating costs in detail
Table 1 assumes that a vehicle operates for 16 hours a day for six days a week at an average speed of 10mph – and hence covers around 50,000 miles per year. Calculating the average fuel consumption and service life of the components, using the data above, the spreadsheet can provide operators with the cost per annum to operate a Euro 4 and hybrid vehicle benchmarked against a Euro 4 Trident.

In addition, the sheet calculates costs over the life of the vehicle, including or excluding major overhaul components, and CO2 saved. Incidentally, the calculation takes into account fuel price rises (using a programmed inflation figure), and the percentage rebate for the BSOG (Bus Service Operators Grant), again programmable. Importantly, it shows that, if we keep BSOG as it currently stands, then the hybrid saves nearly £60,000 over the life of the vehicle. However, if BSOG is discontinued, the result is nearer £130,000.

Clearly, there are engineering and fiscal challenges ahead for bus operators, not the least of which are the performance of batteries and the extra mass from the electric motors and battery pack. Regardless of these, however, looking at the UK as a whole, hybrid buses are likely to become the majority population before long.
Following the London experience, Oxford and Manchester have now taken delivery of hybrid buses, which will enter service by August. With further future developments likely in batteries and electric motors, as well as the humble internal combustion engine, many more cities and towns are likely to follow suit soon.


When red buses go green
Gearing up for the greenest Olympics ever gave London the opportunity to implement an ambitious plan to hybridise its red bus fleet. From when the first buses arrived on the fleet in December 2008, Transport for London (TfL) wanted to involve as many manufacturers as possible, who would trial as many different hybrid offerings as they could. "We split the 56 initial buses in the hybrid fleet among different operators in London to allow them to get experience and knowledge of hybrid buses," explains Mike Winter, fleet development manager at TfL. This meant seven different operators running 10 different routes, using buses from four different OEMs. All the vehicles had different battery types, technologies and theories as to how a hybrid should work most effectively.

The results, says Winter have not been without complications. "Battery and power supply are major factors," he says, confirming that it is most likely that lithium-ion will win out over gel lead acid batteries. "It was quite a task to keep them at the right state of charge, and there were other issues, such as regulating them off and on the vehicle. The initial lead acid battery type has not proven to be the most successful, but manufacturers are modifying these vehicles to put in the latest lithium ion battery packs."

Other problems have seen software systems replaced or upgraded to cope with London's operating conditions, and brand new, smaller diesel engines put in the buses. Winter confirms that these alterations have been made by the bus manufacturers through their own development processes.

He also says that, throughout, electric motors onboard the buses have not given any serious problems. "We have series, parallel and blended hybrids on the fleet, but ultimately they are all driven by electric motors. Some are incorporated into a gearbox, which has a motor inside, but we have had no problems and none have been replaced through wear and tear."

Maintaining the new-look fleet
TfL insisted that manufacturers work to two pre-conditions. One was that the vehicles should look like standard buses. The second was that, from a servicing point of view, continuity must be maintained.

"We asked the manufacturers to provide vehicles that would fit into the standard maintenance systems we operate in each depot," explains Winter. "We have 8,500 buses in London, and to put 56 more in that had to be maintained in a different way across a number of different operators could have led to headaches. So [the manufacturers] had to fit into our standard maintenance procedures, and to date that has been happening."

Hybrid buses are serviced alongside standard vehicles and general maintenance processes are roughly the same, he says – despite the differences in terms of smaller engines and no gearbox. "They are different and are a change to what we are used to, but they have fitted in with the 28-day servicing periods we operate," continues Winter.

Obviously when the service engineer visits the vehicle there are different components to look at, compared with a standard bus. The manufacturers have been responsible for assisting operators here, making sure they are aware of the changes, and highlighting what technicians should be looking for during servicing. The biggest difference is dealing with higher voltages – 660V and 330V for double and single deckers respectively. That is the key issue we have to deal with, but rest assured, the technicians have been trained in how to approach that kind of high voltage system.

Winter is confident that hybrids will continue to make up an ever-increasing percentage of the London fleet. Half a dozen more will take the hybrid fleet to 62 by the end of 2010, rising to 300 by 2011. By 2012, TfL has confirmed that all new models entering service will use hybrid technology. It hopes that the move will ensure the target of a 60% cut in CO2 emissions by 2025 (based on 1990 levels) will be achieved.


Hybrid history from ADL
Alexander Dennis built its first hybrid diesel vehicle in 2003 and it was launched at the 2003 Bus and Coach Show at the NEC in Birmingham.
This vehicle used series hybrid technology with electrical machines from MST. The programme was a success and the vehicle was used as a technology demonstrator up until the beginning of 2008.

Operating the vehicle for half a decade allowed ADL to understand the nuances of hybrid design and operation, which Andrew Boulton says has been invaluable when developing the company's production hybrid systems.

"One of the most important lessons learned was that developing a successful hybrid is about more than just selecting an efficient lightweight motor, generator and battery and then writing a control programme around these devices," he says.

That's why ADL decided to work with a large technology company with the strength in depth to deliver a turnkey system where all of the components have been developed as a package for hybrid bus operation.

Boulton believes that is the route to guaranteeing no compromise in performance and operational life of the equipment, and the integrity of its control software.


Preheating hots up hybrids
Heat exchange specialist Grayson Thermal Systems is one company working on a portfolio of projects for both hybrid drive and conventionally-powered buses and coaches.

Despite a great deal of investment in hybrid propulsion, this firm makes the point that large-scale replacement of existing fleets is not viable, so it is developing systems that can be retrofitted to minimise operators' outlay, yet still bring benefits.

Each is designed to help operators boost performance, cut energy costs and reduce emissions. For example, Grayson is developing a thermal resistor that removes the current requirement for diesel fuel heaters on hybrid drive vehicles (Transport Engineer, January 2010).

"We have been working with a major manufacturer of hybrid drive systems on a project to boost passenger and driver comfort in hybrid drive buses," reveals Grayson managing director Stuart Hateley.

Pre-production models are being evaluated in UK field trials and at Grayson's facility, with an expected production start date of July 2010. "Our research indicates that using the thermal resistor will enable hybrid drive vehicles' diesel engines to warm up faster and to run more efficiently, leading to even lower fuel consumption," asserts Hateley.

Author
John Challen

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