Citroen C4 Cactus Airflow 2L Concept (2014)

These changes can be recognised by their colour and by the materials used. The colour orange identifies all the aerodynamic features and underlines the high-tech character of the C4 Cactus Airflow 2L Concept.

These changes reflect a strong design in which styling contributes to vehicle aerodynamics, reducing vehicle drag for an overall improvement of 20% in aerodynamic performance compared with the production model.

Innovative materials for a lighter weight

The production C4 Cactus is already 200 kg lighter than the Citroen C4, and the C4 Cactus Airflow 2L Concept shaves off a further 100 kg (including the drivetrain). These efforts have therefore reduced the weight of the concept by 11% compared with the production vehicle.

First, efforts to reduce the weight of structural parts: on the C4 Cactus Airflow 2L Concept, the body substructure features new materials:

• aluminium, in particular, for the upper cowl panel, inner side members and rear floor pan,
• high-yield steels for the front side rails and heel board,
• composite materials for the front floor.

These new materials are structural. They help to soak up energy in the event of impact and meet the highest standards in terms of mechanical strength.

This multi-material substructure made it necessary to develop special assembly techniques never used before in the automotive industry. Composite structural parts are a promising field of exploration and will certainly be essential to efforts to make cars lighter in the future. The large-scale production of these parts is one of the high-tech, industrial challenges to be addressed by the automotive sector.

Looking beyond structural parts, extensive studies were conducted on all vehicle parts to reduce the weight of the C4 Cactus Airflow 2L Concept.

Emphasis was placed on lightweight, high-performance materials:

• Carbon-based composite materials were used for the suspension springs, tailgate, rear bench, side panels, roof, roof cross-members, wings and doors. On the lower side sill, wheel arches and lower part of the front bumper, the "textured" look of the carbon brings out the matt appearance of these parts, providing an attractive contrast with the pearlescent appearance of surrounding features.
• Aluminium is used for the engine cradle. The bonnet specifications were the same as for the production C4 Cactus, which already used aluminium.

Owing to their significantly lower bulk density (around 2,700 kg/m3 for aluminium and around 1,200 kg/m3 for carbon compared with 7,800 kg/m3 for steel), these materials contribute significantly to reducing overall vehicle weight.

Given that every gram is important, Citroen also decided to use:

• New processes to reduce the thickness of the tubes and cups of the exhaust line and thus reduce weight.
• Translucent polycarbonate for the panoramic sunroof. This material is even lighter than multi-layer glass but has the same properties in terms of thermal and acoustic insulation and ultra-violet filtering capability.
• Carbon fibres on the Airbumps® to make the material lighter while maintaining its technical properties.

Hybrid Air technology, breakthrough fuel consumption

With its latestogeneration small engines meeting the future Euro 6 standard, the production Citroen C4 Cactus already ranks among the best in its segment with CO2 emissions from 82g/km and fuel consumption starting at just 3.1l/100 km.

The C4 Cactus Airflow 2L Concept goes even further by adopting the Hybrid Air drivetrain. Presented by the PSA PEUGEOT Citroen Group in January 2013 and at the 2013 Geneva Motor Show on the Citroen C3, this technology combines a range of proven sub-systems and technologies: a 3-cylinder PureTech petrol engine, a compressed air energy storage unit, a hydraulic pump/motor unit and an automatic transmission with an epicyclic gear train. An intelligent electronic management system manages input from the driver to optimise energy efficiency.

Three operating modes are available:

• Air power (zero emissions) where the compressed air motor replaces the petrol combustion engine
• Petrol power, using only the combustion engine
• Combined power, drawing upon both the combustion engine and the compressed air.

On the C4 Cactus Airflow 2L Concept, the two compressed air storage tanks are made of composite materials and positioned at the rear of the vehicle.

The PureTech 82 engine, already available on the production model, has been optimised for this new hybrid drivetrain. Friction losses, which account for 20% of the power consumed by the engine, have been reduced in several ways: using a Diamond-Like Carbon coating, making moving parts lighter, and using bearings to guide rotating parts. Further improvements were made by adopting new polymer pads and using very low viscosity oil. Combined with efforts to optimise combustion, overall engine efficiency has been improved by 5%.

Combining the PureTech 82 engine with Hybrid Air technology on the C4 Cactus Airflow 2L Concept reduces fuel consumption by 30% and contributes significantly to achieving a vehicle of 2l/100 km while approaching the PureTech 110 in terms of dynamic performance.

C4 Cactus Airflow 2L Concept, just 2l/100 km

All these advanced technologies together deliver consumption of 2l/100 km. It could therefore be possible, in the medium term, for a vehicle such as C4 Cactus to reach this target.

This very low level of consumption is the result of:

• optimised design with a 20% improvement in aerodynamics
• lower rolling resistance (Tall&Narrow tyres)
• efforts to use lighter parts and thus reduce overall vehicle weight by 100 kg
• the implementation of Hybrid Air technology, which cuts fuel consumption by 30%.

The C4 Cactus Airflow 2L Concept is packed with advanced technologies illustrating the ambitions and ability of Citroen to develop new and innovative responses to the automotive challenges of the present and the future.

TECHNICAL CHARACTERISTICS

• Unladen weight: 865 kg
• Length: 4,156 mm
• Width: 1,729 mm
• Height: 1,487 mm
• CdA: improvement around 20%
• Hybrid Air drivetrain mated to the PureTech engine 82 S&S,
• Tyres: Michelin 155/70/R19