EVO Electric to Demonstrate Plug-in Hybrid Black Cab at Bridgestone Eco-Rally 2010; DuoDrive System with Axial Flux Motor

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Accumulated fuel consumption over Cenex drive cycle for standard London taxi (TX2) and DuoDrive-equipped TX2 (blue line). Click to enlarge.

EVO Electric Ltd., a developer and manufacture of axial flux motors, hybrid drive trains and generator sets (earlier post), will demonstrate a plug-in hybrid version of the iconic London Black Cab featuring EVO’s DuoDrive system at the Bridgestone ECO-Rally on 7 July.

In recent tests, the DuoDrive taxi demonstrated a 56% improvement in fuel economy compared to a standard London Taxi (TX2), and simulations predict that an improvement of 100% is possible with further optimization. Testing was done at an independent vehicle test center, certified by the UK Vehicle Certification Agency (VCA) and part of one of the world’s largest Tier One automotive supplier groups.

This will be the first public demonstration of EVO Electric’s DuoDrive hybrid system, an original powertrain solution for a range of commercial vehicle applications including taxis and delivery vans.

Unlike radial flux motors with a cylindrical rotor turning within a cylindrical stator, axial flux motors use a disc-like rotor sandwiched between two (or facing one) disc-like stator(s). In June, EVO Electric announced that its latest design has a demonstrated peak power density of 5 kW/kg (2.5 kg/kW nominal). (Weight measurements included all motor/generator components including housing, shaft and resolver.)

Representing a 33% increase over the previous generation of EVO motors, the new generation of Axial Flux products offers the highest power density among electric motors currently available for automotive applications, according to the company. This is the design applied in the DuoDrive system.

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DuoDrive system layout. Click to enlarge.

The DuoDrive system is fitted to the taxi by replacing the taxi gearbox with a generator connected to the rear of the engine, a clutch and an electric motor connected to the rear wheels. With the DuoDrive fitted the London taxi can operate in the following modes:

  • Electric vehicle in urban areas. The EVO motor provides the drive and a battery provides power.
  • Hybrid vehicle in urban and extra urban environments. The EVO motor provides drive while the diesel engine and EVO generator provide electrical power to drive the vehicle and recharge the batteries.
  • Diesel vehicle when cruising on the highway. The diesel engine is connected directly to the drive wheels, the EVO motor can provide extra drive power and recapture braking energy, while the EVO generator can recharge the batteries.

With the present engine EVO Electric is confident that 185 gCO2/km can be achieved on the new European drive cycle (NEDC); progressing beyond that would require replacing and downsizing the engine. EVO Electric is actively working on a number of range extender engines that could fulfill this purpose. The development program to do this would follow the successful demonstration of the DuoDrive TX4.

The demonstrator uses a 5 kWh Li-ion battery pack from LiFeBATT, providing an electric range of 15 miles. The architecture of the DuoDrive system allows more battery capacity to be added as required, providing a path to gradually increasing electrification of the taxi fleet.

Now in its fourth year, the ECO-Rally will showcase the latest in low and zero emission vehicle technology in a convoy from Brighton’s seafront to London’s Hyde Park, and will involve some of the biggest names in Formula One driving.


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