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VW Unveils 250+ mpg Wonder

January 26, 2011

VW's long-awaited concept car is now a reality.

No other hybrid car powered by an electric motor / internal combustion engine combination is more fuel efficient. The prototype will be unveiled in a world debut at the Qatar Motor Show (26 – 29 January).

Conceptually, the XL1 represents the third evolutionary stage of Volkswagen’s 1-litre car strategy. When the new millennium was ushered in, Prof. Dr. Ferdinand Piëch, who is today Chairman of the Supervisory Board of Volkswagen AG, formulated the visionary goal of bringing to the market a production car that was practical for everyday use with a fuel consumption of 1.0 litre per 100 km.(about 260 mpg). In the new XL1, Volkswagen is demonstrating that this goal is now within reach.

The most efficient car in the world

The new XL1 shows the way forward for extreme economy vehicles and clean technologies. It also demonstrates that such cars can also be fun. The feeling when driving the XL1 is truly dynamic – not based on pure power, rather on its pure efficiency. Two examples: 1) To travel at a constant speed of 100 km/h, the prototype only needs 6.2 kW / 8.4 PS – a fraction of the performance of today’s cars (Golf 1.6 TDI with 77 kW and 7-speed DSG: 13.2 kW / 17.9 PS). 2) In electric mode, the XL1 needs less than 0.1 kWh (82 Wh/km) to complete a one kilometre driving course. These are record values.

The battery can be charged from a conventional household electric outlet. Naturally, battery regeneration is also employed to recover energy while slowing down and store as much of it as possible in the battery for re-use. In this case, the electric motor acts as an electric generator.

When the full power of the hybrid system is engaged, the Volkswagen prototype accelerates from 0 to 100 km/h in just 11.9 seconds; its top speed is 160 km/h (electronically limited). Yet these numbers alone do not tell the whole story: Since the XL1 weighs just 795 kg, the drive system has an easy job of propelling the car. When full power is needed, the electric motor, which can deliver 100 Newton metres of torque from a standstill, works as a booster to support the TDI engine (120 Newton metres torque). Together, the TDI and E-motor deliver a maximum torque of 140 Newton metres in boosting mode.

Plug-in hybrid concept

With the new XL1, Volkswagen is implementing a plug-in hybrid concept, which utilises the fuel efficient technology of the common rail turbodiesel (TDI) and the dual clutch transmission (DSG). The TDI generates its stated maximum power of 35 kW / 48 PS from just 0.8 litre displacement. The entire hybrid unit is housed above the vehicle’s driven rear axle. The actual hybrid module with electric motor and clutch is positioned between the TDI and the 7-speed DSG; this module was integrated in the DSG transmission case in place of the usual flywheel. The integrated lithium-ion battery supplies the E-motor with energy. The high voltage energy flow from and to the battery or E-motor is managed by the power electronics, which operates at 220 Volts. The XL1’s body electrical system is supplied with the necessary 12 Volts through a DC/DC converter.

Interplay of E-motor and TDI engine: The E-motor supports the TDI in acceleration (boosting), but as described it can also power the XL1 prototype on its own for a distance of up to 35 km. In this mode, the TDI is decoupled from the drivetrain by disengaging a clutch, and it is shut down. Meanwhile, the clutch on the gearbox side remains closed, so the DSG is fully engaged with the electric motor. Important: The driver can choose to drive the XL1 in pure electric mode (provided that the battery is sufficiently charged). As soon as the electric mode button on the instrument panel is pressed, the car is propelled exclusively by electrical power. Restarting of the TDI is a very smooth and comfortable process: In what is known as “pulse starting” of the TDI engine while driving, the electric motor’s rotor is sped up and is very quickly coupled to the engine clutch. This accelerates the TDI to the required speed and starts it. The entire process takes place without any jolts, so the driver hardly notices the TDI engine restarting.

When the XL1 is braked, the E-motor operates as a generator that utilises the braking energy to charge the battery (battery regeneration). In certain operating conditions the load shared between the TDI engine and the electric motor can be shifted so that the turbodiesel is operating at its most favourable efficiency level. The gears of the automatically shifting 7-speed DSG are also always selected with the aim of minimising energy usage. The engine controller regulates all energy flow and drive management tasks, taking into account the power demanded at any given moment by the driver. Some of the parameters used to realise the optimum propulsion mode for the given conditions are: accelerator pedal position and engine load, as well as the energy supply and mix of kinetic and electrical energy at any given time.

Two-cylinder TDI uses mass production technology: The 0.8 litre TDI (35 kW / 48 PS) was derived from the 1.6 litre TDI, which drives such cars as the Golf and Passat. The 0.8 TDI exhibits the same data as the 1.6-litre TDI common rail engine in terms of cylinder spacing (88 mm), cylinder bore (79.5 mm) and stroke (80.5 mm). In addition, the XL1’s two-cylinder and the mass produced four cylinder share key internal engine features for reducing emissions. They include special piston recesses for multiple injection and individual orientation of the individual injection jets.

The excellent, smooth running properties of the common rail engines were transferred to the two cylinder engine. within addition, a balancer shaft that is driven by the crankshaft turning at the same speed optimises smooth engine running.

Meanwhile, the TDI’s aluminium crankcase was constructed to achieve high rigidity and precision, which in turn leads to very low friction losses. With the goal of reducing emissions, exhaust gas recirculation and an oxidation catalytic converter as well as a diesel particulate filter are used. Equipped in this way, the 0.8 TDI already fulfils the limits of the Euro-6 emissions standard.

 

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