15 September 2005
This year’s International Motor Show (IAA) in Frankfurt was marked by a wider, albeit seemingly reluctant, adoption of hybrid technology by European car manufacturers, who traditionally preferred the conventional diesel in their quest for energy-efficient powertrains. Among announcements from several manufacturers (including Porsche, VW, and BMW) DaimlerChrysler unveiled two hybrid concepts utilizing diesel and gasoline directly injected (GDI) engines, rather than the more common stoichiometric gasoline engine.
The diesel powered model—the “Bluetec Hybrid”—utilizes a 3.0 liter V6 diesel fitted with urea-SCR aftertreatment system for NOx control, thus indicating a relevance for the US market. The GDI concept—the “Direct Hybrid”—uses a V6 gasoline engine with spray-guided direct injection. Both models use the same mild hybrid transmission (which is different from the two-mode GM-DaimlerChrysler hybrid currently under development).
The Direct Hybrid 3.5 liter 4-valve V6 GDI (gasoline) engine generates an output of 215 kW (292 hp) at 6,000 rpm, and a maximum torque of 365 Nm from 2,400 rpm. The spray-guided combustion system relies on piezo injectors and high pressure (200 bar) fuel system. For NOx control, the engine employs exhaust gas recirculation and NOx adsorber aftertreatment. Fuel consumption is 8.3 l/100 km (34 mpg) over the NEDC test. A 6 kW electric motor installed between the engine and the automatic transmission can function as a starter or a generator, and can provide additional boost (up to 250 Nm upon ignition, 50 Nm at 1000 rpm) during startups and other points of operation.
The same electric motor is used in the Bluetec Hybrid, which is powered by a 3.0 liter V6 diesel (a variant of the 320 CDI) that delivers 173 kW (235 hp) of power and a maximum torque of 540 Nm between 1,600 and 2,400 rpm. The combined power and torque for the hybrid is 179 kW (243 hp) and 575 Nm, respectively. Fuel consumption is 7.7 l/100 km (36.7 mpg)—a 20% improvement over a comparable conventional diesel.
Both gasoline-electric hybrids and conventional diesels can provide a fuel consumption improvement. However, as argued by a number of European manufacturers in the past, the fuel savings from hybrids can be realized only under urban stop-and-go driving conditions, while diesels provide fuel economy benefit under any operating conditions, including highway cruising. The diesel-electric powertrain would be the most fuel efficient, but also the most expensive.