The hybrids deliver average combined city and highway fuel consumption of 3.4 liters per 100 kilometers (69 mpg US), with 90 grams of CO 2 emitted per kilometer—a tank-to-wheel record for compact cars, the most popular segment in Europe. This is about 25% better than a similar vehicle equipped with a gasoline hybrid system, or as much as a liter per 100 kilometers in combined city and highway driving.

As promised, PSA Peugeot Citroën unveiled two prototypes featuring diesel-electric parallel hybrid powertrains, the Peugeot 307 and the Citroën C4 Hybride HDi.

Hybrid technology using a petrol engine is not very competitive financially, and does not offer significantly better fuel economy or CO 2 emission performance than a conventional HDi diesel engine. However, PSA Peugeot Citroën believes that combining a hybrid powertrain with an HDi engine would constitute a step change in terms of improved fuel economy and lower CO 2 emissions in Europe, where diesel engines are already widely used. —PSA Peugeot Citroën statement

PSA Peugeot Citroën’s Hybrid HDi technology includes:

1.6-liter HDi engine and diesel particulate filter system (DPFS)

New-generation Stop & Start system (earlier post)

Electric motor and inverter

High-voltage battery pack

Dedicated control electronics

All-electric mode for speeds under 50 kilometers an hour (31 mph)

Driver selection of Extended ZEV (Zero Emission Vehicle, i.e., all-electric) mode

Electronically-managed gearbox

PSA Peugeot Citroën Parallel Hybrid Architecture. Click to enlarge.

The engine. The prototype marks the first combination of the 1.6-liter, 66 kW HDi engine with the latest generation Stop & Start system. The company added a dedicated control system to the engine, using operating instructions coordinated directly by the powertrain management unit (PTMU), most notably for engine starts and stops, while also guaranteeing delivery of the torque required by the driver.

The engine, with the diesel particulate filter system (DPFS), meets Euro-4 standards.

Stop & Start system. The Stop & Start system used in the Hybride HDi powertrain is based on the technology integrated in both the Citroën C2 and C3. The new system has 40% more power than the first generation to support the easier starting of the 1.6-liter diesel.

In the hybrid powertrain, the Stop & Start system restarts the ICE. While the Stop & Start function is only used on the C3 when the vehicle is stationary, the engine stop function can occur at any given moment on the Hybride HDi, as soon as the vehicle’s speed falls below 60 kilometers an hour (37 mph).

Electric motor and inverter, The synchronous permanent magnet electric motor develops 16 kW of continuous power, with 80 Nm of torque. It offers peak power of 23 kW and 130 Nm to meet occasional demand from the driver.

PSA Peugeot Citroën opted for the volume and performance of the motor to ensure that the all-electric mode would be used for speeds up to 50 kilometers per hour—a speed typical of city driving.

Connected to the inverter, the motor operates in a voltage range from 210 to 380 volts. In the restricted space available, this electric motor/inverter does not enable use of the conventional engine cooling circuit, whose typical temperature is too high. Water cooling is therefore provided by a special radiator and a low-temperature cooling circuit at 60°C.

For main road and highway driving, the electric motor can provide a 35% power boost for extra acceleration.

Battery system. The battery pack consists of 240 NiMH (Nickel-Metal Hydride) cells that deliver 23 kW of power at a nominal voltage of 288 volts. The cells are cooled by special air intakes that recover air from the passenger compartment, taking advantage of its temperature control.

There is also a conventional 12V storage battery, which continues to handle its usual functions.

The high-voltage battery pack fits in the rear part of the Group’s platform 2 vehicles (base for the Peugeot 307 and Citroën C4) in place of the spare tire, following a slight modification to the cut-out in this compartment. Adding the batteries does not reduce trunk capacity for any of the vehicles.

All-electric mode: Zero Emission Vehicle (ZEV). The driver can use a special switch to access an extended all-electric mode that expands the operating range for the vehicle in this mode. In this case, the ICE is only activated for more prolonged acceleration.

The extended all-electric mode is de-activated either automatically, when the high-voltage battery pack no longer has a sufficient charge, or manually, by using the dedicated switch.

Economics and Future. PSA Peugeot Citroën says that while it could market its Hybride HDi vehicles as early as 2010, the introduction is dependent upon its ability to make the technology available at an affordable price.

Today, the price gap between a Hybride HDi model and a comparable diesel HDi model is still too wide and would have to be halved to make diesel hybrid vehicles accessible to most consumers.

The Group is planning a two-pronged approach to reach that goal:

Extensive R&D on the four areas that generate most of the extra cost: high-voltage batteries, electric motor/generator, inverter and the regenerative braking system.

Unite the expertise of equipment manufacturers and research laboratories to focus on this project.

PSA Peugeot Citroën has asked the French Agency for Industrial Innovation to support the project.