Emissions statement

A full-hybrid diesel vehicle claims to have cut carbon emissions by 30 per cent compared to the standard showroom model. The prototype Citroën Berlingo Multispace emits just 99g/km of CO2 after being radically modified by Ricardo, with input from Qinetiq.

‘The project has highlighted a range of technologies capable of delivering ultra-low CO2 without compromising vehicle function and performance,’ said Ricardo’s chief engineer Dave Greenwood.

The government-backed Efficient-C ultra-low carbon car project team used a 23kW motor supported by a 288V lithium-ion battery to boost fuel economy of the 1.6 litre common rail diesel to more than 75mpg. Automated manual transmission, regenerative braking and a starter-alternator allowing engine stop-start have helped to minimise fuel consumption.

Alain Klein, director of hybrid vehicle development at PSA Peugeot Citroën, was optimistic about the achievement. ‘We are delighted with the results which demonstrate the potential for a step change in CO2 emissions reduction with a diesel parallel hybrid,’ he said.

The low emissions have been achieved by using a sophisticated energy management system to control all the elements of the hybrid transmission. ‘Your right foot is connected via the pedal to the hybrid control system, not to the throttle,’ said Prof Neville Jackson, Ricardo’s technical director.

Among the system’s many functions is one to ensure the engine is not used when the electric motor would do the job more efficiently. Typically this happens when both engine speed and torque are low.

Developing the system has required many resources. ‘The control algorithms that deliver the hybrid’s seamless transitions between motor and engine amount to 70MB of code,’ said Greenwood. ‘That’s on top of the standard 30 or 40MB needed to manage a good diesel engine system.’

The system has to work six different operating modes, the simplest being the engine driving through the clutch and gearbox to the wheels.

The second mode is when the motor absorbs torque from the engine to generate electrical energy which is stored in the battery for later use. When the Berlingo needs an acceleration boost, power is released from the battery so the motor gives extra torque to the wheels.

In the fourth mode, the electric motor alone draws power from the battery. When the vehicle brakes, kinetic energy is captured by the motor and stored in the battery. The sixth mode is when the car is stationary and the engine generates electricity which is stored in the battery.

Several supporting systems have been put in place to allow these different modes. A low-temperature cooling system protects the motor and power electronics. A DC/DC converter provides 12V power from the 288V system because it is more efficient than generating at 12V directly.

And electrically-driven ancillary systems are used in place of mechanical ones, including 12V electro-hydraulic power steering, an electric vacuum pump for braking assistance and electric aircon. The Berlingo can travel up to 10km in electric mode alone.

The Berlingo may seem an unlikely choice for such an advanced project, but at the time it started Peugeot Citroën was changing its model line-up. ‘Also the car was more challenging than standard five-door C-class models because it does not have the same aerodynamic characteristics,’ said Greenwood. ‘And during development, it had a lot of interior space to accommodate vital monitoring and testing equipment.’

Private cars are responsible for 15 per cent of the UK‘s CO2 emissions, so even small reductions will help the government towards meeting its Kyoto commitments. That’s why the Department for Transport contributed almost £1.5m towards the £3m budget for the two-year project.

But the design is unlikely to be mass-produced for some time. The price of materials and manufacturing means the thrifty Berlingo would have to sell for £3,000 more than the current version. PSA Peugeot Citroën’s vice-president for innovation, Robert Peugeot, said: ‘We seek to develop technologies affordable to a wide majority of the public, so we must bring back the increased cost to around £1,400 to allow a mass-market distribution.’

Efficient-C is the first result from the DfT’s £10m ultra-low carbon car challenge announced in 2003, managed by the Energy Savings Trust. Projects must produce a C-segment five-door vehicle with CO2 emissions of 100g/km well-to-wheels. Two other projects received funding although one, from MG Rover, did not progress beyond the feasibility study before the company went into administration. The other, from Zytek, is due to be completed next year.