Automotive designers MIRA have unveiled a retro-fit hybrid conversion that unlocks the potential to save 61% on fuel costs and lower tailpipe emissions by 39% without designing a new car. The hybrid conversion with a novel removable battery pack upgrades existing vehicles to the technology some concept cars are showcasing at this year's motor shows. A technology demonstrator has been built around a popular b-segment car to show the potential of the technology. As a "plug-in hybrid" the vehicle can charge its batteries by running its engine or by plugging into the mains. Plug-in hybrids are at the vanguard of new vehicle design; yet MIRA has taken the idea one step further to make the concept far more practical and useful for motorists.

As a concept evaluation tool the Hybrid 4 wheel drive Vehicle (H4V) was never destined for public sale, so the project received support through the Energy Saving Trust's Low Carbon R&D programme which is funded by the Department for Transport.

Philip Sellwood, Chief Executive of the Energy Saving Trust, which is managing the initiative said: "This project has designed a new system allowing hybrids to be more flexible and practical for every day use. With over 20% of the UK's total carbon emission produced by road transport every year, these advances in technology are vital. Over 80% of people believe that climate change is having an impact on the UK right now, so it is important to bring more technology like these to the market place."

Derek Charters, MIRA's Advanced Powertrain Manager explains the rationale behind the project: "Despite advances in powertrain technology you can still obtain electricity from your domestic provider far cheaper and greener than you can produce it via an automotive combustion engine, so 'plug-in' hybrids make sense. With this project we've removed the primary limitation of the 'plug-in hybrid' concept by allowing the battery pack to come to the mains, rather than having to park right next to a socket ...which is more than a little difficult if you live in a terraced house or flat."

The H4V project was conceived to show just what's possible with a regular car and some specialist knowledge. Derek explains further: "MIRA's hybrid vision is to lower tailpipe emissions and deliver better fuel efficiency than an equivalent diesel, at a diesel level 'on-cost'; whilst delivering driver delight features such as an EV mode and "two-pedal" town driving."

This is precisely what MIRA have done with H4V. The demonstrator vehicle is based on the popular Skoda Fabia, instantly differentiating itself from the standard model by the unique H4V badge and 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 though MIRA's clever e-differential. Overall, the H4V differentiates itself from the standard model by returning 64mpg2, as measured on the EU drive cycle. Whilst general levels of performance, such as top speed and acceleration are similar to standard.

The car boasts a battery pack arranged into 3 portable cassettes, each capable of storing 30KW. These storage units could also power external devices, including a range of lifestyle accessory items. The very latest nano-particle technology has been applied to increase the energy density of the already 'high-tech' Lithium Ion Phosphate batteries. This ensures the energy pack is as lightweight and compact as possible, whilst delivering superior voltage stability over the charge range. The same Li-Ion Phosphate battery technology is evident in the separate low voltage circuit used to start the engine, insuring the car's impeccable 'lead free' green credentials.

The battery pack in one of the key ingredients of a modern hybrid. With so much effort and expense being invested in the battery pack it makes sense to use it in as many places as possible, not just the car itself. The ultimate aim of the project team is to see the power pack transferred from the car into a range of other devices, which could include camping equipment for SUV variants, or redeployed to power electric jet skis or quad bikes.

Despite the impressively green credentials, headline grabbing hyper-economic mpg figures were never the aim for H4V - to do that the team would logically select a more frugal base vehicle. The selection of the base car is largely unimportant, as far as the technology is concerned; so long as the donor vehicle's specification included modern features, such as a throttle by-wire system and some other basics, to avoid duplicating unnecessary workload. The project code of H4V, standing simply for 'a' Hybrid 4wd Vehicle re-enforces the generic nature of the upgrade.

A 39% improvement is beyond what most traditional hybridisation systems would normally deliver, so MIRA have retuned the engine and created a custom calibration that works in harmony with the electrically driven axel to deliver additional synergies beyond the simple fuel savings possible via 'torque-neutral' hybridisation schemes.

A regenerative braking system makes its debut on a MIRA hybrid. Derek explains why: "The viability of such systems requires careful analysis to ensure that the mass penalty is outweighed by the energy recovery potential. The technology has now matured to deliver a tangible economy benefit, not just a 'feature' for the marketers."

The frugal powertrain is supported by a new aero pack, further reducing drag by 8% to achieve a Cd of just 0.299. Aerodynamics makes only a small contribution to EU drive cycle calculations, due to the cycle's overall low speed character, so it's often marginalised by those wishing to bias development towards attributes that make the most difference at low speed. Thankfully, MIRA's approach goes some way to deliver a vehicle that lives up to consumer expectations on real roads.