PSA Peugeot Citroen's Hybrid Air incorporates a longitudinally mounted central pressure tank for energy storage (colored blue), with an hydraulic storage tank (blue) at the rear. The central tank is pressurized to 300-400 psi (20-27 bar), according to Bosch.
If 3 L/100 km fuel consumption (approximately 78 mpg U.S.) once seemed an unlikely target for a practical, high-volume production car, 2 L/100 km (117 mpg U.S.) would have been laughable. But possibly no more, with PSA Peugeot Citroën’s unveiling of its heavily patented Hybrid Air technology, a full hybrid system that the company regards as “a key step towards the 2 L/100 km car by 2020.”
With the looming prospect of achieving Europe's 95 g/km (4.1 L/100 km or 57.6 mpg U.S.) fleet CO2 emissions target within a similar timescale, PSA decided on a radical approach. The automaker is now developing a potential solution via the combination of a gasoline engine and the use of compressed air accumulated via energy recovery during a vehicle’s deceleration phase.
Potential average CO2 reduction compared with a comparable conventional vehicle would be 30% and possibly 45% for urban use. PSA engineers believe the system should prove highly cost-effective compared to present production hybrid powertrains.
Simpler, lighter, cheaper than a battery HEV
Although the configuration will need to be extensively developed with regard to its systems integration, it would combine what PSA’s Executive Vice President of R&D, Guillaume Faury, describes as “tested technologies.” They include the engine (possibly a three-cylinder gasoline unit, though a diesel would also be suitable); a compressed air energy storage unit; an hydraulic pump/motor unit positioned alongside the engine; and an automatic transmission of so far unspecified type.
Potential weight saving compared to a regular hybrid layout could be up to 100 kg (220 lb).
Smart electronics to manage it all would be at the core of the system. The production target is "quite soon," Faury said, which translates to about three years. An example is slated for next month's Geneva Motor Show.
The company is working very closely with its suppliers. Bosch, a PSA engineering ally, will co-develop the new system, which the supplier calls "a hydraulic hybrid powertrain.” Giving some detail of the system, Bosch stated that it comprises two hydraulic units and their respective pressure accumulators.
The power-split provides for three aspects—conventional mechanical; hydraulic; and a combination of both for maximum accleration or to meet high load requirements such as steep gradients.
Kinetic energy generated when decelerating/braking is converted into hydraulic energy and stored in the accumulator for vehicle propulsion as required, including when moving away from rest and for relatively brief periods in town, a role that a battery would fulfill in a conventional hybrid.
PSA sees the system as particularly appropriate for small/compact cars, but it would also have a role for light, urban delivery vehicles.
New engineering management process
A significant aspect of the Hybrid Air program has been PSA’s “One Team, One Project” philosophy for managing innovation of this type. Some 200 specialists have been working cohesively, with expertise spanning powertrain management to marketing. Because it was a beyond-the-horizon project (and under the aegis of a specific Board member), those involved were encouraged to adopt new, more flexible mindsets.
All appropriate Strategic/Tier One suppliers were treated as partners to create an inter-relationship that would see value generated from the absolute beginning of the project (its initial engineering and design phase).
In the context of this strategic partnership, Peugeot launched the 3008 HYbrid4 in 2011, the world’s first series-produced diesel-electric hybrid passenger car with an axle-split (also called through-the-road) powertrain. In close collaboration with Bosch, PSA Peugeot Citroën developed the electric motor, power electronics, and high-voltage generator as well as the special technical design of the ESP required for hybrid vehicles.
This powertrain concept now also features in PSA’s Peugeot 508 (both the RXH station wagon and the HYbrid4 sedan) and Citroën DS5 HYbrid4 models. Bosch also supplies the components for the electrical powertrain of those models.
PSA's new global modular platform
Complementing the announcement of the Hybrid Air project, PSA gave a preview of its new global modular platform, designated EMP (Efficient Modular Platform) 2. As well as modularity, its raisons d’etre include solutions concerning equipment and carbon reduction. Also presented was selective catalytic reduction (SCR) technology. SCR will be introduced to production models this year, with the aim of getting diesel NOx levels down to those of comparable gasoline engines.
EMP2 facilitates considerable configuration flexibility, explained Faury. It includes four track widths; five wheelbases; two cockpit and cowl solutions; two rear suspension architectures (deformable and multilink); various rear unit modules for different seat layouts; and enhanced manufacturing flexibility. The latter includes a fully robotized body shop and 55 vehicles-per-hour capability.
Eventually, EMP2 will be used by half of all new Peugeot and Citroën models internationally and will also have a role within alliance partner GM’s vehicles. The platform brings a significant weight reduction, averaging around 70 kg (154 lb), utilizing high-strength steel, composites, and aluminum. Processes will include hot forming, flexible rolling (to facilitate variable material thicknesses), hydroforming, and laser welding.
Increased vehicle efficiencies enabled by the EMP2 architecture will be complemented by use of SCR aftertreatment. “These efforts to achieve a significant reduction in weight and CO2 emissions will deliver an average 22% decline in fuel consumption for EMP2 vehicles,” said Faury. These will be in the C and D vehicle segments.
Technologies that will be part of the EMP2 picture will include motorized brake calipers; electric power steering (EPS) with city-park facility; isolated engine cradles to cut running noise; ESP compatible with other electronic safety chassis assistance; quieter bearings; and facia-mounted cooling, which will also feature off-center cooling for the turbocharger.
Styling will also benefit from the new platform, with shorter front overhangs achieved via a compact front module, with the center of the wheels moved forward to aid the use of larger wheels. Floor and ride height will be lowered by as much as 20 mm (0.80 in) and under-hood space better packaged.
PSA has revealed further technologies that it is developing including a light city EV with a power consumption level of 85 W·h/km; a plug-in hybrid that would undertake most travel in zero-emission mode; and a new exhaust gas recirculation system.