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UK Collaboration Develops Plug-in Hybrid Retrofit for Conventional Vehicles

Battery pack state of charge vs. distance for the ADDZEV vehicle under all-electric power on the UDDC cycle. Source: Cranfield. Click to enlarge.

A collaboration led by the UK’s Cranfield University has developed a retrofit plug-in hybrid conversion system for a conventional internal combustion engine vehicle. The Affordable Add-on Zero Emissions Vehicle (ADDZEV) technology demonstrates how it may be possible to convert segment of the existing the UK vehicle fleet into plug-in hybrid vehicles using a through-the-road approach. (Earlier post.)

Developed to reduce the carbon emissions of inner-city driving, the ADDZEV system was developed using a standard Vauxhall Combo van. The development team retained the existing conventional front-wheel-drive system of the Combo but added an electric drive, powered via low-cost valve regulated lead-acid (VRLA) batteries, to the rear wheels.

This transformed the van into a hybrid vehicle capable of achieving an all-electric range of more than 20 km (12 miles) on one charge.

The ADDZEV consortium includes:

  • Cranfield University. Project lead, control and vehicle integration;
  • European Advanced Lead Acid Battery Consortium. Project management and battery procurement;
  • Millbrook Proving Ground Ltd. Integration, vehicle packaging and testing;
  • Provector Ltd. Development of battery and drive electronics management systems; and
  • University of Oxford. Electric machine design and manufacture, drive system development and integration.

The ADDZEV project team believes that, due to simulation studies using real-world data from a range of vehicles, the technology could be scaled up for larger vans and even city buses.

The ADDZEV system uses twin liquid-cooled motors with a maximum power of 100 kW and peak torque of 350 N·m for maximum gradeability, mounted in a discrete sub-frame under the rear floor of the vehicle. Electric only drive has been limited to propel the vehicle at a speeds up to 60 km/h (37 mph).

For out-of-town driving or higher speed operation, the existing front-wheel-drive diesel power unit provides conventional operation. It can also be configured to switch manually between modes, enabling selection of ultra low emission operation in a low emission zone or city center.

The approximately 4.8 kWh battery pack is charged through specially-devised control software and power management systems created by Cranfield University and Provector. The operational strategy takes the state of charge in the pack down to 40%. Drivers have two options for charge—either by connecting to the electricity grid or via the internal combustion engine that generates and stores energy when the vehicle is in motion.

This results in a typical operating cost for fuel in a small delivery business that could be reduced by 40% compared to operation on traditional fossil fuels alone. The technology, which can be retro-fitted onto a wide range of vehicles, has performed well in final testing at Millbrook, according to the partners.

Conducted as part of the Low Carbon Research and Development program run by the Energy Savings Trust (EST), the project was jointly-funded by the Department for Transport and the European Advanced Lead Acid Battery Consortium.




You could retrofit BAS+ or wheel hub motors on a lot of different cars. The question, as always it seems, is what would it cost and what is the payback period? Without subsidies, it might cost $5-10k and payback in 5 years or more. Now we can ask, if the government paid for some of it through tax credits, how many other people would do it?

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