BMW is set to introduce its third production hybrid following in the tire treads of the ActiveHybrid 7 and soon-to-cease-production ActiveHybrid X6. The new ActiveHybrid 5 is BMW's first 5 Series hybrid and is based on the company's 535i sedan. It combines that car's 225 kW/306 hp 3.0-liter TwinPower Turbo inline six-cylinder engine with a 40 kW/55 hp electric motor for a combined output of 250 kW/340 hp. This allows the ActiveHybrid 5 to go from zero to 100 km/h (62 mph) in 5.9 seconds and limits fuel consumption to between 6.4 and 7 liters per 100 km (44 to 40 US mpg).
Offering the choice of electric power, combustion engine, or combination of both, the ActiveHybrid 5 can be driven on electric power alone at up to 60 km/h (37 mph) for local emission-free driving in urban areas. Electric-only range is limited to around four kilometers (2.5 miles) at an average speed of 35 km/h (22 mph), however. When the driver seeks more power, the ICE is engaged automatically, with power from the two drive systems transferred to the rear wheels by the eight-speed automatic gearbox.
When stationary, a hybrid start-stop function shuts down the ICE to save on fuel. Once the driver releases the brake, depending on the battery's current charge level and how much power the driver is asking for, the vehicle will restart on either the electric motor alone or the electric motor and the ICE. Additionally, the ICE will also shut down and be fully decoupled from the drive shaft when coasting at speeds of up to 160 km/h (100 mph) in ECO PRO mode.
As is standard in hybrid vehicles, the ActiveHybrid 5's electric motor acts as a generator during braking and coasting to recharge the vehicle's lithium-ion battery pack. However, when accelerating, the electric motor also takes on a boost function to provide a burst of power to assist the ICE.
The vehicle's power electronics are also linked with the standard-fitted navigation system so - depending on the available data - the vehicle can take into account upcoming driving conditions to prime the drive components for maximum efficiency. For example, if the system knows the car is approaching a hilly section, it can devote all the battery's electrical energy to provide supplementary power as it knows the battery will be able to recharge on the subsequent descent.
The synchronous electric motor is integrated into the housing of the eight-speed automatic gearbox and its operating temperature is regulated by the combustion engine's cooling system. Meanwhile, the lithium-ion battery is positioned between the wheel arches in the luggage area for maximum protection and has its own cooling system. BMW says this reduces the load capacity of the ActiveHybrid 5 to 375 liters (99 US gal), which is 145 liters (38 US gal) less that of a conventional Series 5 sedan.
BMW will be delivering the ActiveHybrid 5 to U.S. dealers from March 2012.