It has been a long time coming, but PSA Peugeot Citroën is now manufacturing the world’s first production car with a hybrid diesel powertrain. Designated HYbrid4, it is offered in the crossover Peugeot 3008 and comprises a 2.0-L, front-mounted, 120-kW (161-hp) HDi diesel engine (Euro 5) plus a rear positioned 27-kW electric motor with maximum torque of 200 N·m (145 lb·ft) driving the rear axle to achieve all-wheel-drive capability. Its best combined fuel consumption figure is 3.8 L/100 km, with CO2 emissions of 99 g/km.
The powertrain will also be installed in the Peugeot 508 RXH SW (station wagon) next year and in Citroën’s DS5. The technology, which is extensively patented, may also be adapted by other OEMs. PSA Peugeot Citroën has strong powertrain links with BMW, although neither company has confirmed this possibility.
Gaetan Demoulin, Chief Test Engineer for the program, confirmed that PSA had spent five years developing the hybrid: “It was a little longer than usual to meet our many criteria because this car is something entirely new in automotive architecture. We made sure that it achieved the systems’ efficiency and performance that we required, particularly regarding fuel consumption.”
A significant part of the development, carried out in partnership with Bosch, was that the four central components of the axle-split technology for the 3008 were production-ready for 2011 introduction. Overall design of the system was down to PSA Peugeot Citroën, with Bosch responsible for the synchronous electric motor and associated controls. Bosch also developed a specific ESP solution for the 3008 hybrid. Regenerative electric drive on the rear axle was restricted to safeguard vehicle stability in all conditions.
The car’s motor is compact and fits a 180-mm (7.1-in) diameter by 120 mm (4.7 in) long space. Its power rating is 20 kW at speeds up to 7500 rpm. The water-cooled SMG 180/120 separator-motor-generator is rear-mounted. The axle-split hybrid uses a nickel-metal hydride (Ni-MH) battery, also placed at the rear.
The biggest development challenge, said Demoulin, was to ensure that the hybrid had a very significant combined fuel consumption margin over the comparable 3008 model with 2.0-L diesel engine and six-speed manual gearbox, which achieves 5.4 L/100 km.
A salient contribution to efficiency was the use of a six-speed automated manual gearbox. Peugeot decided that, at its target market level, an auto box was necessary but did not want to fit a power-sapping torque-converter system. Extensive development of the transmission has resulted in shift quality markedly smoother (up and down) than most examples of what is a compromise technology. Demoulin said he regards a majority of automated manual gearbox levels of shift quality as “unacceptable”—but not that of the new hybrid.
NVH was also a challenge for the hybrid development team. “Again, this was because we set high standards, with the Stop&Start system a major part of that,” explained Demoulin. The car has a high voltage (8-kW peak) starter/alternator system designated Bosch 138/80. “It provides a restart time of 400 milliseconds and can supply the power requirements of the electric motor if required (if the high-voltage battery is discharged) when in all-wheel-drive mode. We worked on the development of the hardware and logic of the Stop&Start system from the beginning of the HYbrid4 program. Some systems will not operate efficiently below +2°C, but the alternator we use can achieve engine restarts at -3°C.”
Although the use of a 1.6-L diesel might have provided even better fuel consumption, PSA elected to use a 2.0-L unit to deliver performance figures deemed necessary for the 3008’s category and particularly to meet customer expectations for the 508RXH. However, the engine’s maximum torque of 300 N·m (221 lb·ft) is 50 N·m (37 lb·ft) less than its application in other vehicles.
The HYbrid4 system offers four modes, actuated via a rotary switch on the center console: auto, ZEV, 4WD, and sport. Auto does what it says—allows the entire integrated system to react automatically, with the electric motor adding power and torque for maximum acceleration. From 120 km/h (75 mph), power comes solely from the engine, and the rear axle is disconnected from the powertrain.
ZEV gives all-electric drive for up to 4 km (2.5 mi) and is driver-selectable. A downside to its operation is a cut-out of the air-conditioning compressor, noticeable quickly in slow traffic despite the system’s inertia. If cabin temperature exceeds a set level, the diesel engine and compressor restart automatically to cool the cabin.
Manual selection of all-wheel drive provides SUV levels of capability, but it is not designed for seriously challenging off-road use, while sport mode makes for faster gear shifting and higher revs in the lower gears plus the combination of engine and electric motor.
A core element of the electric drive is the HPCU (Hybrid Power Control Unit). The power electronics comprise the control software for both electric motor and the hybrid management; the HPCU also operates as a pulse inverter. It acts as a direct-current converter between the 3008’s low-voltage electronic system and the electric motor’s high-voltage network. It needs to process currents up to 340 A at up to 300 V in a 12-L (730-in³) volume.
The production of a dual inverter that functions as a link between a high-voltage battery and two electric motors (drive motor and starter/alternator) is a “first” for Bosch, but the company managed to package it in the same volume as a single inverter, said Dr. Matthias Küsell, Bosch’s Vice President, Development and Customer Projects Hybrid and Electric Vehicles. “Conditions were already pretty cramped for our earlier inverters; the new dual inverter takes that to a whole new level.”
Performance figures for the 3008 Hybrid4 include a 0-100 km/h (0-62 mph) time of 8.6 s and an electronically limited top speed of 191 km/h (119 mph).