World's First Affordable Diesel Hybrid Powertrain

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Zytek Hybrid

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As the vehicle is a plug-in hybrid, an on-board charger has been fitted that can recharge the hybrid battery in under seven hours from 0-100% SOC (state of charge). The charging system is mounted in the spare wheel well under the battery and should not need servicing. The other key power component, the inverter, is mounted under the bonnet, close to the electric motors to minimise electrical losses. It's innovative, software-managed current control system is used for both DC and AC machines, providing vehicle manufacturers with substantial design flexibility and the possibility of component sharing across different architectures.

As well as supplying the 300V three phase power for the motors, Zytek's inverter supplies 1,800W of 12V power for the vehicle's electrical systems.

The battery can be charged in three ways: via regenerative braking to efficiently capture the vehicle's kinetic energy instead of dissipating it as heat; via the engine driving the starter/alternator to generate electricity; and by plugging the vehicle in to a conventional domestic 13Amp electrical socket using a connection hidden under the rear numberplate. Two additional safety pins on the plug, which is carried with the vehicle, disable the powertrain while it is connected to the mains supply.

Further fuel consumption savings have been achieved by replacing parasitic systems with more efficient and controllable electrically driven systems. When the engine is running, the flow of coolant is much more closely controller via use of an electrically-driven water pump, only consuming power when necessary. The brake vacuum pump has been supplemented with an electric pump so braking assistance can be provided even when the engine is off.

There is also a 6kW electric water heater to provide cabin warmth when the vehicle is operating as an electric vehicle, and a 5kW electric air conditioning compressor to provide all the cabin cooling requirements.

The electric water heating element is also used to dissipate energy when the batteries are full and the vehicle is slowing using regenerative braking. This helps the engine and cabin heating system warm up more quickly and provides a more consistent brake feel. "An important objective for this vehicle is that it is totally ready for production," says Cheeseman. "It has the design detail and sophistication needed to enter the market immediately."

Driving the Zytek dual-mode hybrid

The driver of the Zytek dual-mode diesel hybrid can choose from standard or high regenerative braking and can also select one of three control calibrations:

• 'Economy' is ideal for city driving. Use of the engine is minimised and maximum power is limited to increase the range on pure electric power.

• 'Drive' is ideal for mixed usage. Full power is available and the engine will automatically stop/start when appropriate.

• 'Sport' disables the stop/start function and allows maximum power and acceleration

The high regen mode is available in all of the above calibrations, allowing the driver to store more regenerative energy, giving even greater fuel economy and lower emissions.

The sophisticated control system makes powerblending imperceptible to the driver, with acceleration from zero to maximum with no torque interruptions. Acceleration from zero to 62mph (100kph) takes just 12 seconds and the car can cruise comfortably at highway speeds. With perfectly balanced corner weights, the vehicle's dynamics are also comparable with the standard car. In all ways, the Zytek dual-mode diesel hybrid offers the driving experience of a conventional small family car.

Summary

Zytek's contribution to the Ultra Low Carbon Car Challenge has created a new hybrid powertrain technology that for the first time makes ultra-low carbon emissions affordable in the most popular classes of vehicle. Using zero emissions electric drive and energy from an overnight recharge, the vehicle can make a return journey across London's extended congestion charge zone for just eight pence. The innovative dual-mode diesel hybrid comfortably exceeds all the targets set by the ULCCC, with better performance and lower emissions, and is ready for applications engineering to bring it to production.

"For the first time, we have a simple, affordable hybrid solution. And it's British," says Stephen Hart, transport programme manager with the EST. "This is a considerable achievement. There is currently no production diesel hybrid and nothing that meets comparable cost targets. With Zytek's technology, I can see this changing fairly soon."

Performance data

• Standard vehicle Zytek dual mode hybrid Fuel economy (Urban) 5.9l/100km, 47.9 mpg No fuel used in electric drive

• Fuel economy (Combined) 4.6l/100km, 61.4 mpg 3.2l/100km, 88mpg (corrected to charge neutral, ie with no net change in battery state of charge)

• Overall CO2 (Tank-wheel) 121g/km 85g/km Acceleration 0-100kph 15.53s Under 12s

• Maximum speed 155kph 155kph (limited) www.zytek.co.uk

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