EFFICIENT powertrains are the future. A 2,0-litre engine powering a large, luxury SUV may have been unthinkable a couple of years ago, but that’s exactly what I experienced when I recently drove the new generation BMW X5 eDrive plug-in-hybrid electric vehicle (PHEV) prototype at the Miramas proving ground in Marseille, France. Thanks to the fact that the 70 kW electric motor offers up all its torque immediately, responses from the eDrive’s throttle inputs were near-instantaneous. When stepping on the accelerator pedal a bit harder, the new 2,0-litre turbopetrol engine joined in seamlessly and added another 180 kW. The combined power of BMW’s X5 PHEV is more than 200 kW and results in a claimed zero to 100km/h time of less than seven seconds and a top speed in excess of 200 km/h. To call the eDrive’s performance adequate is an understatement when the claimed fuel consumption is a miserly (if slightly optimistic) 3,8 litres per 100 km on the new European drive cycle (NEDC). BMW has showcased its most recent and future technologies under the banner of Efficient Dynamics. These and other building blocks will be found in the hybrid vehicles of tomorrow.
A key ingredient to a hybrid is an efficient internal combustion engine. BMW showed its new range of Efficient Dynamics (ED) engines which will power its hybrid and conventional vehicles into the future. The modular, inline engine range (500 cm3 cylinders) consists of a 1,5-litre three-cylinder, a 2,0-litre four-cylinder and a 3,0-litre six cylinder unit – all turbocharged in both petrol and diesel. Thanks to construction commonality within a combustion type (petrol or diesel), the proportion of shared components has increased by as much as 60%, while design commonality between petrol and diesel engines is approximately 40%.
This concept is similar to Volvo’s Drive-E engine range (only 2,0-litre four cylinder engines) but owing to the wider performance envelope across Mini and BMW products, different capacities are needed. By increasing the application of aluminium and magnesium in the production of these engines, a substantial weight saving is achieved over the outgoing range.
The petrol engines will feature direct injection, variable valve timing and lift and turbocharging. The diesel units will feature a variable nozzle turbo (VNT) and state-of-the-art, high pressure, common rail injector systems. These technologies are all bundled under BMW’s TwinPower concept. To further increase the efficiency of the petrol engines, BMW added watercooled exhaust manifolds that enable quicker warm-up times because the hot exhaust gas warms the coolant in the circuit. Another advantage is that under full load, the engine can still run close to the ideal fuel/air ratio (lambda one) as enrichment is not required to protect the exhausts and catalysts downstream from excessive heat (upwards of 950 degrees Celsius). Although more applicable to cold climate countries, engine encapsulation, which pertains to powerplants that are covered by insulation material to help retain residual heat when the vehicle is parked, allows quicker heat-up on restart and also aids noise insulation.
The electrical system of a hybrid vehicle will consist of a battery pack, electric motor and control hard- and software. The advantage of a hybrid vehicle is that its battery pack and electric motor can be downsized compared with an EV because it’s not the vehicle’s only energy and power source. In the X5 prototype, the 9 kWh battery pack is located under the boot board and the 70 kW electric motor in the bell housing of the transmission. The advantage of BMW’s intelligent all-wheel-drive (xDrive) system is that kinetic energy can be recouped from all four wheels under braking and the division of torque between the axles can be varied as needed. An on-board charger is provided to charge the battery pack when it’s plugged in.
Because the X5 is an existing vehicle, BMW did not have the luxury of creating an all-new body for the eDrive PHEV (as Toyota did for its Prius, for example). What the Munich-based brand did instead was to tweak the design in a few places to lower the drag of the vehicle. The main visual changes include small flaps in front of the wheels to direct the air round the wheels, vents in the front bumper to create an air curtain around the front wheels, pressure release vents to the rear of the front wheel arches to release air pressure, aero blades on the sides of the rear window and an integrated edge on the rear taillamps to reduce the vacuum effect at the rear. The result is a Cd figure of only 0,31 which is best-in-class for a large SUV.
PHEV OPERATING MODES
To get the best efficiency out of hybrid powertrains, innovative energy control algorithms are essential. Electric power should be used whenever possible as it is the most efficient (and cost-effective) operating mode. Therefore, in a PHEV, it’s important for the system to know where the next charging point will be on your journey as to maximise all available electrical energy in getting the vehicle to its destination. GPS data will analyse the inclinations of your selected route and calculate the most efficient energy balance up to 10 km in advance. If no route is selected, the system will attempt to calculate where the driver is heading; for example, the normal commute to work and back and base its computations on historic data.
It seems plug-in-hybrid vehicles are the best interim modes of automotive propulsion as the motoring world transcends from fossil fuel to electric powertrains. It is, however, not a perfect solution because the combination of two sets of technologies does increase the complexity, cost and mass of a vehicle. The excellent claimed fuel economy figures are a result of the test procedure on the European drive cycle (NEDC) where the stored electrical energy in the battery pack does skew the figures to the advantage of hybrid vehicles. Until vehicles such as the BMW X5 eDrive go into production in 2015, we will not know how the concept will fare in real-world conditions. We are, however, in favour of all technical developments that will improve vehicle emissions while still meeting our automotive needs.
ED engine range performance envelope
|1,5-litre, 3-cyl||70-85 kW/220-270 N.m||55-170 kW/150-320 N.m|
|2,0-litre, 4-cyl||110-140 kW/330-400 N.m||135-190 kW/280-400 N.m|
The quest for hybrid efficiency
BMW displayed the following additional current and future efficiency enhancing technologies
Light-weight carbon-fibre tech-nology for wheels, propshafts and structural parts.
Laser-light technology with advanced lighting ability and reduced power consumption (see Techtalk).
Energy recovery from heated cabin air before it leaves the cabin to enhance electric range.
Predictive gearshifts by monitoring traffic conditions with front- and rearward-facing radars to predict overtaking or merging manoeuvres. The correct gear will both enhance the vehicle’s response and reduce fuel consumption.