BMW Shows Plug-In Hybrid Electric Based on X5 Sports Activity Vehicle

June 1, 2014

Paul Weissler

BMW's forthcoming plug-in hybrid electric vehicle (PHEV), based on the X5, reflects a combination of high performance and sophistication in its approach to controls and features. The 2.0-L twin-scroll turbo delivers 240 hp/179 kW (255 lb·ft/ 346 N·m). And combined with the 95-hp electric motor, there's a peak output of 270 hp (201 kW) and 300 lb·ft (407 N·m). The power goes through BMW's continuously engaged X-Drive (intelligent All Wheel Drive) system, so the X5 maintains its "SAV" (Sports Activity Vehicle) character. The "concept" vehicle was introduced at the New York Auto Show; the production version is expected within the year.

The PHEV control system provides several intelligent modes, including a predictive one based on the route plugged into the vehicle's navigation system. There is also a battery temperature control system for high ambient temperature operation that uses an electronically controlled tap off the vehicle's air conditioning.

Estimated NEDC ratings

The estimated all-electric range is 30 km (19 mi), based on a BMW study that 80% of trips with the X5 are under 20 mi (32 km). That range doesn't include the effects of electric A/C operation in hot weather or use of resistance heating in cold weather, although the cabin temperature can be preconditioned while the X5 is plugged in. The EV distance was measured on the NEDC (New European Drive Cycle), on which this X5 also received an estimated CO₂ rating of just 89 g/100 km. The fuel-economy number on the same cycle is just under 3.8 L/100 km (62 mpg).

The X5 has a 9 kW·h lithium-ion pouch-type battery pack (96 cells total in 12 packs of eight cells), and is programmed to deplete only to 3 kW·h. The 3 mi (4.8 km) per kW·h for the 6 kW·h is a reasonable expectation for the estimated all-electric range without climate control. The plug-in recharge time with BMW's recommended home unit, called Wallbox Pro, could be under an hour, as the unit's maximum hourly charge rate is 7.4 kW.

The hybrid drive goes through an electric clutch, and an eight-speed automatic, on which the torque converter and its clutch has been deleted but which contains other clutching elements.

Three primary modes

The X5 PHEV offers a choice of three primary modes: Eco Pro, Comfort, and Sport. In a brief test drive, SAE Magazines was able to operate the vehicle in all three modes, and although our passenger from calibration engineering said he still had work to do, the performance levels and transitions were smooth. In Sport, for example, the full-throttle produced a powerful combination of both engine performance and acceleration assist from the electric motor. This mode also includes a recalibration of the gas pedal software for an aggressive response.

The Comfort setting's hybrid operation is called "Auto E." The vehicle always starts in electric drive for a smooth rolling start, and with a light foot on the gas pedal, the X5 can stay in electric drive up to just over 40 mph (64 km/h). Then the engine will start and the vehicle will go into an intelligent hybrid operation, with more or less EV in the combination, depending on road speed, engine load and climate control operation.

The driver can select a Save Battery mode to maintain the full charge for later, pure EV operation, which is driver-selectable and called MAX eDrive. That choice could be used to run the X5 as an EV in cities that limit use of conventional vehicles during certain periods. The system will take the battery pack down to its minimum (3 kW·h). Even in the MAX eDrive to mandate EV operation, the X5 can run at speeds up to 75 mph (121 km/h) with the eight-speed automatic

Eco Pro is an intelligent hybrid drive mode, with a throttle tuned for lower response. The software picks the type of operation—engine, EV, or hybrid as the driving conditions change, to maximize fuel efficiency. It's tied in with "ConnectedDrive," a predictive-navigation trip-planning system that looks at the selected destination and analyzes the topography en route. "ConnectedDrive" considers the posted speeds and determines what combination of hybrid operation will be the most efficient, or even if there is a section (perhaps heavy traffic) where EV-only operation provides the most efficient result. If there is an area where EV-only operation is required, it will ensure there is enough battery capacity for it, and show locations of charging stations on the navi screen. Although there are no such restrictions presently in place, BMW pointed out that some cities are considering it, and in Amsterdam there are free parking facilities with battery charging, vs. normal in-city parking fees of $85-90 (U.S.).

There is a possibility for battery pack recharging by the vehicle in motion, from low power demand situations, such as long downgrades with regenerative braking, and this can add to or maintain pack capacity. There also may be conditions in which the engine is running and for higher engine efficiency more load is desirable. In that case, the engine could recharge the battery pack. In Eco Pro, the electric motor does not provide a performance-assist function (as in Sport); it only operates to reduce fuel consumption.

Battery pack cooling

The battery pack, which is under the cargo area floor, is kept within a temperature range of -35 to +40°C (-31 to +104°F). In hot weather, the battery pack is cooled when necessary to ensure long life, by engaging an active air conditioning-based cooling system. First, an electronically controlled zone valve on the X5's A/C is opened. This allows refrigerant flow through a separate line into a second system within the battery pack housing. The refrigerant passes through an expansion valve and then into a serpentine evaporator within a plate housing between the cell assemblies, which are stacked—one group atop the other. The refrigerant vaporizes in the battery pack evaporator, absorbing heat from the cells and then flowing to the front, where it joins the primary flow from the passenger cabin and goes to the A/C condenser. At present, the system is using R-134a, and because the X5 is made at BMW's plant in South Carolina, there is at present no legal compulsion to use a low global warming alternative refrigerant for models sold in the U.S., although there are Corporate Average Fuel Economy credits. And as the X5 is a continuing vehicle, it also may use R-134a in Europe until 2017. BMW said no decision on an A/C system changeover had been made. There is no active heating system in cold weather. A BMW engineer said that the vehicle pre-conditioning charge, and then the normal discharge and recharge during operation would be sufficient to deal with that issue.

Air conditioning use, of course, impacts the EV driving range, and within the Eco Pro mode there is a menu on the control stack screen that encourages fuel-saving. A line graph indicates level of Eco Pro potential—0 to 100% with two selections, a speed warning "tip" and a reduced level of climate control. If the driver checks the box and sets the speed warning "tip: low enough (we tried 50 mph/80 km/h), the potential went to 100%. With a higher speed "tip" (we also tried 80 mph/129 km/h), but a check of the climate control reduction, the driver gets a 50% rating.

---