The most efficient car in the world

 

Future mobility is one of the most stimulating topics of our time. The key question here: Just how much could the energy consumption of cars be reduced if all the stops were pulled out for efficiency? There is now an answer to this question, and Volkswagen is delivering it in the form of the new Volkswagen XL1 Concept. Combined fuel consumption: 0.9 l/100 km. No other hybrid car powered by an electric motor / internal combustion engine combination is more fuel efficient. Conceptually, the Volkswagen XL1 represents the third evolutionary stage of Volkswagen's 1-litre car strategy. 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 liter per 100 km. In the new XL1, Volkswagen is demonstrating that this goal is now within reach.

The new Volkswagen XL1 attains a CO2 emissions value of 24 g/km, thanks to a combination of lightweight construction (monocoque and add-on parts made of carbon fiber), very low aerodynamic drag (Cd 0.186) and a plug-in hybrid system − consisting of a two cylinder TDI engine (35 kW/48 PS), E-motor (20 kW/27 PS), 7-speed dual clutch transmission (DSG) and lithium-ion battery. The results: with fuel consumption of 0.9 l/100 km, the new Volkswagen XL1 only emits 24 g/km CO2. Since it is designed as a plug-in hybrid, the XL1 prototype can also be driven for up to 35 kilometers in pure electric mode, i.e. with zero emissions at point of use. In the new Volkswagen XL1, wing doors make it easier to enter and exit the car. Further progress has been made by manufacturing body parts from carbon fiber reinforced polymer parts (CFRP), a technique used in Formula 1 car construction. Once again, Volkswagen has successfully achieved significant reductions in production costs - an important step forward to make viable a limited production run of the XL1. Background: together with suppliers, Volkswagen has developed and patented a new system for CFRP production in what is known as the aRTM process (advanced Resin Transfer Mounding).

 

The new Volkswagen XL1 Concept 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:

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).

In electric mode, the Volkswagen XL1 needs less than 0.1 kWh (82 Wh/km) to complete a one kilometre driving course. These are record values.

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 turbo-diesel (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 Volkswagen 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 Concept on its own for a distance of up to 35 km. In this mode, the TDI is decoupled from the drive train 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 Volkswagen 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 minimizing 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 realist 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 Volkswagen XL1 Concept'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 balance shaft that is driven by the crankshaft turning at the same speed optimizes smooth engine running.