Take charge

Electric hybrid powertrain technology that allows batteries to be removed from vehicles for recharging would end the need to plug cars directly into the mains, claims its UK developer.

Automotive research group MIRA said the system, which can be retrofitted to existing vehicles, could make hybrids more accessible to a wider range of consumers.

Although the urban market with its stop-start driving is ideal for electric hybrid vehicles the cars must be recharged via mains electricity, making their use impractical for those living in flats or terraced housing without dedicated parking outside their homes.

The MIRA system, currently fitted to a Skoda Fabia demonstrator called the Hybrid 4-wheel drive Vehicle (H4V) features a novel removable battery pack, which can be lifted out and recharged before returning it for use. However, the vehicle could still be plugged into the mains directly when this is possible.

Its developers claim the design has the potential to save 61 per cent on fuel costs while lowering emissions by 39 per cent, as measured on the EU drive cycle. It can deliver fuel consumption of 64mpg, and retains similar acceleration to a petrol vehicle.

The project has been jointly funded by MIRA and The Energy Saving Trust's Transport Technology Programme.

Derek Charters, MIRA's advanced powertrain manager, said the technology concept was originally developed as part of work with MG Rover. However, after the company went out of business MIRA took the unusual decision to develop the system without a project partner.

A Skoda Fabia was chosen as it was easy to work on and had a modern engine system. 'We have worked on Skodas before and know well how the onboard computer worked,' he said.

Although the cells are portable, MIRA now hopes to reduce their weight further, with an aim of reaching 10-15k. This will be achieved by reducing the number of cells while maintaining 330v.

'The biggest challenge is deciding the distance people need to travel in electric vehicle (EV) mode,' said Chambers. 'Although some people might say 10 miles is not a good range, when the car moves at over 30mph the engine will kick in and you don't travel large distances in an urban environment.'

He said the aim of the project was to lower exhaust emissions and deliver better fuel efficiency than an equivalent diesel at around the same cost.

The H4V also features some aerodynamic modifications. The 50/50 hybrid derives power jointly from a 60kw petrol engine at the front and two 35kw inboard motors powering the rear wheels.

The car boasts a lithium ion phosphate cell battery pack arranged into three portable cassettes, each capable of storing 30kw. The latest nano-particle technology has been applied to increase the energy density of the cells.

This is claimed to ensure the energy pack is as lightweight and compact as possible, while delivering superior voltage stability over the charge range. The same Li-Ion phosphate battery technology is used in the separate low voltage circuit used to start the engine.

MIRA has also re-tuned the engine to create a custom calibration that works in harmony with the electrically driven axle to deliver additional synergies beyond the simple fuel savings possible via torque-neutral hybridisation schemes.

The demonstrator features regenerative braking and the powertrain is supported by a new aero pack, reducing drag by a further eight per cent.

Chambers said that the system would also reduce engine wear. 'I dislike some hybrid vehicles as the engine is constantly stopping and starting, which isn't good for it,' he explained. 'In our vehicle it runs for a minimum of a minute once it has been started.'

Although the vehicle will not be going into production, MIRA is looking to work with SMEs who could exploit the technology for manufacture, or attract the interest of automotive companies.

Julia Pierce

Comments

Comments - The following comments have been posted in response to this article

Several comments regarding hybrid vehicles. Firstly, the fuel economy given is notably worse than the SEAT Ibzia Ecomotive that returns 88mpg using a conventional diesel powered internal combustion engine. Secondly, the weakness of the present generation is the need to carry the dead weight of the battery when using the engine, and the dead weight of the engine when using the battery. As demonstrated by PML Flightlink in Hampshire, using a BMW Mini car with a 250cc engine, four 160hp motors, one for each wheel, and a generator, provides the means to always power the car by electrical energy. The engine runs at an optimum speed for maximum efficiency, drives a generator, the output of which powers the four electric motors. Braking is regenerative, where the energy is placed into a fast charge battery. This battery is used to start the engine, as provided in a conventional car, and to provide the initial kick when accelerating from a standing start. In terms of performance, 0 to 62mph takes 4.5 seconds, with a top speed of 150mph and 80mpg for the fuel consumption. I consider the present generation of hybrid vehicles to be poor when compared to what PML Flightlink have demonstrated, and the length of time that the automotive industry has taken to achieve what the railways have been doing for more than half a century. As noted before, an idea that is well over 50 years old, taken from the railway industry.
Andrew Porter: 09 May 2008

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