Hybrid pioneers [hybrid electric vehicles]

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    20-Sep-2016

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    PIONEERS

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    " A pressures on car manufacturers to d m a t i d y mduce COr emissions are starting to bear fruit. In Europe alone, CO, emissions for petror and diesel fleets have been W g , on average, by 1.9% a year since 1995. This equates to a fuel consumption figure of 165g/km, compared to #e European Automobite Manufacturers Association (ACEA) target of 1Wkm by 2008.

    The reductions to date have been achieved through the wider use of diesels and incremental improvements zn existing technologies, such as the common-rail diesel engine. Howevef, further significant savings will only be possible with a fundamental shfl in vehicle powertrain technology. In

    the short term, this is l i e l y to involve the wider use of hybrid vehicles; in the longer term, it could lead to the jettisoning of the internal combustion (IC) engine and the wholesale switch to fuel cells as the primary automotive power source.

    TORQUE BOOSTERS The growth in the capabilities of control, power electronics and electrical machines has given birth to hybrid electric vehicles like Toyota's Prius and Honda's Insight. Here, overall efficiency is increased by using an electric motor to boost the IC's torque performance at low revs.

    The Prius, outwardly a conventional family saloon, achieves a combined fuel consumption of 57'6mpg thanks to a 33kW electric motor operating in conjunction with a 53kW petrol engine. Cumulative worldwide sales for the Prius currently exceed 1oO,OOO, whilst Toyota expects to be selling 300,000 hybrids a year by 2005.

    Hybrids already have a loyal following- Holywood's Leonard0 DiCaprio and Cameron Diaz are Prius owners-but there are drawbacks. In comparison to a car powered solely by an IC engine, a hybrid needs a specialised electric motor, a high- capacity battery (to power the electric motor and to store the energy produced by regenerative braking), a range of ancluary power electronic systems (to manage the battery and supply power to the electric motor), plus an elaborate high-level control system to ensure that all these units +

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  • .. 44 - The i-MoGen is built around a Ricardo- developed high-output (74kW) 1 . 2 litre diesel engine. Poor lOW-reVS torque performance is a particular problem with small diesels, which the i-MoGen addresses by using motor assistance between 1000 and

    AS BATTERY TECHNOLOGY IMPROWEE THE HYBRID WEHICLE CAN BE EXPE TO GAIN A STEADILY INCREASING SHARE OF TOTAL CAR SALES work seamlessly together. Inevitably, all this com- plexity adds significantly to the vehicle's costs, and Toyota is believed to have lost up to $3000 on every Prius sold during the first four years of sales after December 1997.

    Nevertheless, a s battery technology improves, leading to lower costs and longer life, the hybrid vehicle can be expected to gain a steadily increasing share of total car sales. Ricardo, the UK-based specialist automotive consultancy, is predicting that IC-based hybrid vehicles will achieve 6% market penetration by 2010, rising to 25% market penetration by 2020.

    THEMILDAPPROACH With the electric motor sued to provide up to 40% of the full power output, the Prius is an example of a full hybrid. But, at the 2001 Frankfurt motor show Ricardo and the automotive component manufacturer Valeo announced a 4 million joint development programme to produce a technology demonstrator of a novel hybrid, the i-MoGen (intelligent motor generator), in which the electric motor's contribution to total power would be less than lo%, a so-called mild hybrid deaign.

    pmgrers tawardr the European Automobile Manufaaurerr Association's 2008 target for [Source: Ricardo]

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    I t European petrol fleet I 140 r

    --D . European diesel fleet -*.total

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    ................................................... .. currently 165g/km target of 14og/km by 2008 I , I I I I - 1 120 I

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    2200rpm. The i-MoGen doesn't employ a dedicated ancillary motor as such; instead it kills two birds with one stone by using a Valeo 42V integrated starter-alternator operating in motor mode.

    The completed i-MoGen-based on a Vauxhall/Opel Astra-took to the road towards the end of last year, and has subsequently been demonstrated to 23 vehicle manufacturers. The performance has stunned many observers: fuel consumption is 4 litres per lOOkm (lilmpg), and zero to 100km/h takes just 12 seconds. Richard Gordon, Ricardo's chief engineer, attributes the i-MoGen's Prius-rivalling results to "using diesel (higher energy content per litre of fuel), and up-rating the engine so that most of the vehicle's power comes directly from the fuel'- the essence of mild hybridisation.

    Overall, fuel consumption is reduced by 28% compared with the 2 litre diesel engine normally used in the Astra donor vehicle. Ricardo attributes 20% of this figure to the intrinsic efficiency of the downsized diesel engine combined with fast warm-up and intelligent cooling.

    A further 5% reduction is provided by regenerative braking, while the 'stop and go' function, which was made possible by the use of a 42 V power rail and the starter- alternator, delivers 3% in fuel savings.

    The cost, bulk and weight of the battery system is a major issue in hybrid vehicle design. Mild hybridisation means that the i-MoGen is able to able to make substantial savings in the scale and cost of the battery system. It uses a Saft air-cooled NiMH battery rated at 9kW, 620Wh capacity and weighing 17kg. In comparison, the Insight's battery module weighs 22 kg and has a capacity of around 9OOWh. As an added bonus, the i-MoGen's battery is small enough to be located in the spare wheel well.

    Ricard Gordon is optimistic about the mild hybrid's prospects: "Due to their

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    convention; VI icle platform, mild hybrid technology will be a significant sales reality by the end of the decade.

    FINAL SOLUTION? Looking into the future, the fuel cell offers the promise of cars with essentially zero emissions-at the point of use at least- and every major motor manufacturer is spending huge sums on fuel cell development. Ford launched its first FCV (fuel cell vehicle) in 1997, and later this year a small fleet of third-generation Ford Focus FCVs will taking to the roads of the US as part of a programme to establish the benefits of FCV hybridisation.

    Fuel cell efficiency falls as ontput increases-almost the opposite problem of the internal combustion engine-and the Ford FCVs battery is used to increase efficiency by augmenting the power output of the fuel cell at high speed and under rapid acceleration. Theres an echo of the i-MoGen here, as both vehicles achieve the benefits of hybridisation without the need for an auxiliary electric motor, although from diametrically opposed ends of the technology spectrum.

    Primary power for the Ford FCV is provided by a Ballard Mk 902 proton exchange membrane fuel cell module, designed specifically for integration into passenger vehicles and rated at 68kW (92hp). This operates at a relatively modest 85OC, allowing it to be positioned directly underneath the seats of the driver

    and the front seat passenger Hydrogen for the fuel cell is stored in a 178 litre tank located in the cars boot. The gas is compressed to around 350bar (5OOOpsi), so that the tank can hold nearly 4kg of hydrogen, which, in energy terms, equates to approximately 15 litres of petrol. At low deceleration rates, the electric drive operates as a generator, supplying energy to the 216Y 1140Wh battery According to Ford, up to 95% of all braking incidents result in energy generation.

    The FCVs hybrid design, combined with some 300kg in weight savings, results, according to Ford, in an overall efficiency of more than 60%, i.e. three to four times that of a car powered solely by an internal combustion engine. The car can accelerate from zero to 100km/h in 13.5 seconds, has a maximum speed of 128km/h (deliberately capped) and a range of more than 300km.

    INTERESTING TIMES IC-based hybrids are a proven technology; The fuel cell-augmented by hybridisation or otherwise-suffers from high costs and problems of fuel supply; Ford envisages that, sometime after 2010, it will be able to offer fuel cell vehicles to customers at affordable prices and that hydrogen filling

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    Top: The i-MoGen is based on a standard Vauxhall/Opel M a

    Middle: Valeos 6kW crankshaft-mounted, intergrated statter- alternator

    Battom: The iMoGens NiMH 620Wh battery fits mnvenientlv into the cars spare hee l well

    stations, if built in sufficient number, will produce fuel at a price comparable to existing petrol prices. The Ricardo viewpoint, as expressed by Nick Owen, Ricardos senior manager in the Technology Group, takes a more qualified view of the fuel cells prospects: For the next twenty years, hybrid technology will achieve far greater sale volumes than fuel cell vehicles, as it is much more compatible with todays manufacturing and servicing infrastructure. For the longer term, fuel cells, as prime movers or auxiliary power units, remain an interesting, low-emission alternative to the IC engine.

    Either way, the technological focus of the motor car is undergoing a fascinating shift, with a one-time emphasis on mechanical design giving way to a design environment where electrical and software engineering skills are increasingly at a premium. It sounds like interesting times ahead. W