Automotive Intelligence - the web for automotive professionals and car enthusiasts
March 08, 2012
In the new Cross Coupé, MQB elements for a future generation of SUVs – in this case, the MQB front and rear suspensions, 140 kW / 190 PS TDI of the new EA288 engine series and a 6-speed DSG. They were merged with electrical components that are also "made by Volkswagen", and they include the lithium-ion battery in the centre tunnel, front E-motor with 40 kW and rear E-motor with 85 kW.
Intelligent networking of drive systems
Zero emissions thanks to electric motors. In pure electric mode – in this case its speed is limited to 120 km/h –, the concept car can cover up to 45 km. This is sufficient driving range for most of the world’s commuters to drive to work with zero emissions. In pure E-mode, the driver can choose whether the focus should be on optimising electric driving range or dynamic performance. This is implemented by the combination of E-mode and CITY mode and the combination of E-mode and SPORT mode. In the electric driving range maximising E-mode (CITY), only the E-motor on the rear axle powers the car. In the dynamic E-mode (SPORT), the electric drive system powers both the rear and front wheels. In pure electric driving, the turbodiesel is decoupled from the drivetrain by disengaging the clutch, and it is shut off. The clutch on the gearbox side remains closed, and the 6-speed DSG is engaged. The E mode is activated by pressing what is knowna s the EV mode button (EV: electric vehicle) next to the gear shift lever. The Cross Coupé then drives like a purely electric vehicle. Even during fast driving, the internal combustion engine is not engaged, provided that the battery is sufficiently charged. As soon as the power of the TDI is needed again, either because of the battery’s charge state or other parameters, the engine engages without any jolt, and it is once again actively coupled to the drivetrain within fractions of a second.
Battery in the centre tunnel. In pure electric driving, the E-motors are supplied with energy from a lithium-ion battery that consists of eight modules. The battery has an energy capacity of 9.8 kWh and is located in the centre tunnel of the Cross Coupé. Power electronics operating at a voltage of approx. 370 Volt, which is integrated in the front engine compartment, manages the flow of high-voltage energy to and from the battery and the electric motors. Meanwhile, the 12 Volt electrical system is supplied with power via a DC/DC converter. The electric drive system does not impose any space limitations on the interior. The battery can be charged either from external power sources (230 Volt connection) or while driving.
Charging also at push of a button. The driver can intentionally switch to CHARGE mode (by pressing another button next to the gear shift lever) to charge the battery via the TDI engine while driving. This mode might make sense, for example, if the driver wishes to drive in certain designated environmental zones that might be toll-free for electric vehicles operating with zero emissions. The momentary electric driving range and total range of the Cross Coupé are continually displayed in the instruments. An engine controller regulates the overall energy and drive management system under consideration of the specific load demanded by the driver. The driver can choose from a total of five driving modes: CITY (an eco mode with minimal fuel consumption), SPORT (high dynamic performance), OFFROAD (continuous all-wheel drive), E-mode (pure electric driving) as EV-CITY or EV-SPORT, or CHARGE (via the TDI). In parallel, the Cross Coupé utilises different operating states, in which the motors/engine and drive axles are coupled or decoupled as a function of driving needs:
Zero emissions by ‘sailing’. As soon as the driver lifts his or her foot from the accelerator, both electric motors and the engine are shut off and decoupled from the drivetrain – provided that the battery is sufficiently charged. This is referred to as ‘sailing’. Zero emissions are generated in this case as well.
Zero emissions in battery regeneration mode. If the driver takes his or her foot off the accelerator pedal or brakes, and the battery is not sufficiently charged, the two electric motors are operated as generators to feed energy recovered from braking into the lithium-ion battery. The TDI is also shut off and decoupled in this operating state.
Boosting. When driving should be especially sporty in nature, the E-motors form an alliance with the TDI. In the professional jargon of the hybrid world this joining of forces is known as ‘Boosting’. The Cross Coupé is driven by all four wheels in this mode.
Offroad with ‘electric propshaft’. As soon as the driver chooses to activate OFFROAD mode, all four wheels are once again driven. However, in this mode the front electric motor, now supplied with energy by the TDI, is the sole source of electrical power for its counterpart at the rear axle. Since the energy for the rear electric drive is by wire and does not flow mechanically, this is referred to as an ‘electric propshaft’. Since the TDI powers the rear electric motor via the front electric motor in OFFROAD mode, the all-wheel drive system is fully functional, even if the lithium-ion battery is in a low charge state.
Driving with the TDI. If the TDI is powering the vehicle by itself, the Cross Coupé is a pure front-wheel drive vehicle. In driving states in which greater fuel efficiency is possible by load boosting, the E-motors act as generators to charge the battery. When all of the on-board energy reserves are utilised, the vehicle’s combined fuel consumption value is 1.8 l/100 km; the vehicle’s 55 litre fuel tank thus enables a theoretical driving range of 1,287 km.
(March 06, 2012)