|Powertrain of the 102EX. Click to enlarge.|
Rolls-Royce Motor Cars is unveiling the 102EX, a one-off, fully electric-powered Phantom, today at the Geneva Motor Show. (Earlier post.) The car will tour during 2011, serving as a testbed to gather research data which will be used in informing future decisions on alternative drive-trains for Rolls-Royce Motor Cars. The global drive program will include Europe, the Middle East, Asia and North America.
The Phantom Experimental Electric (EE) features the car’s aluminium spaceframe. However, the naturally aspirated 6.75-liter V12 petrol engine and 6-speed gearbox have been replaced by a 71 kWh lithium-ion battery pack and two electric motors mounted on the rear sub-frame. These motors are connected to a single speed transmission with integrated differential.
Each motor is power rated to 145 kW, giving Phantom EE a maximum power output of 290 kW and torque of 800 N·m (590 lb-ft) available over a wide band. This compares with 338 kW for standard Phantom with maximum torque of 720 N·m (531 lb-ft), delivered at 3,500 rpm.
The Li-ion cells use a nickel cobalt manganese chemistry with a gravimetric capacity of around 230 Wh/kg, a high energy density which is important in achieving an acceptable range between re-charges. Peak current from the pack is 850A, delivered at 338 VDC. Pre-launch tests suggests Phantom EE should run to a range of up to 200 km (124 miles), with top speed limited to 160 km/h (99 mph). Acceleration from 0-60 mpg takes less than 8 seconds.
The Phantom EE battery pack houses five modules of pouch cells, a 38-cell module, a 36-cell module, and three smaller ones of ten, eight and four arranged in various orientations within an irregular shaped unit. This resembles the overall shape of the original engine and gearbox.
Each of the 96 cells was individually tested before assembly into modules to determine their characteristics and capacity. Sub-assemblies were further tested under load to verify that the power connections between each cell perform to specification.
The electronic sensing units for each group of cells were tested and calibrated prior to assembly and put through a rigorous temperature cycling regime designed to provoke failure of weak components. The main electronic box, which contains the switching and control gear, was tested in isolation from the other components to verify correct operation.
Three separate charger units (3kW each) are fitted to the battery, which allow both single-phase (20 hours) or three-phase charging (8 hours); for a passenger car this is unique. A fourth induction charger is also fitted to enable wireless charging, a technology being trialled in Phantom EE.
The battery pack would be expected to last over three years were it to be used every day. Part of the program however will be to test this assumption in a real world environment and deliver a more robust answer to the question of battery lifespan.
As part of the Phantom EE project, Rolls ROyce will test induction charging, allowing re-charging to take place without any physical connection, delivering greater convenience for owners and hinting at the potential for a network of remote charging facilities.
There are two main elements to induction charging; a transfer pad on the ground that delivers power from a mains source and an induction pad mounted under the car, beneath Phantom EE’s battery pack. Power frequencies are magnetically coupled across these power transfer pads.
The system is around 90% efficient when measured from mains supply to battery and it is tolerant to parking misalignment. For example, it is not essential to align the transmitter and Phantom receiver pads exactly for charging to take place. While pads are capable of transmitting power over gaps of up to 400mm, for Phantom EE the separation is in the region of 150mm.
The coupling circuits are tuned through the addition of compensation capacitors. Pick-up coils in the receiver pad are magnetically coupled to the primary coil. Power transfer is achieved by tuning the pick-up coil to the operating frequency of the primary coil with a series or parallel capacitor.
The pick-up controller is an essential part of the technology because it takes power from the receiver pad and provides a controlled output to batteries. It is required to provide an output that remains independent of the load and the separation between pads. Without a controller, the voltage would rise as the gap decreases and fall as the load current increases.
The transmitter pad has been constructed to shield magnetic fields to prevent EMI egress to bystanders and the system operates well within internationally agreed limits.
This is the first application of the technology in a GKL++ segment (super luxury vehicles priced at more than €200,000) and the battery pack is thought to be the largest ever fitted to a road car, according to Rolls.
Evaluation of the technology is an important part of the test program. However, more fundamentally, the car will seek answers to questions posed of Rolls-Royce owners: what their needs might be for the future considering factors such as range, performance and re-charging infrastructure.