Volkswagen L1 Concept (2009)

VW L1 Concept

The Volkswagen L1 Concept is unique in the world today. Thanks to a carbon fibre reinforced plastic (CFRP) body, it weighs just 380 kilograms. The two-seater is powered by a new common rail turbo-diesel (two-cylinder TDI) and an electric motor. With its average fuel consumption of 1.49 litres diesel per 100 kilometres, this fully road-ready and extremely aerodynamic L1 (Cd 0.195!) is advancing to become the most fuel-efficient hybrid automobile in the world. CO2 emissions of the 160 km/h fast concept car are just 39 g/km. If the Volkswagen L1 were to also go into production in 2013, it would debut an entirely new lightweight car concept and introduce a new era in automotive production.

Drivetrain

The TDI, E-motor and 7-speed DSG are located at the rear, and they combine to create the most fuel efficient road-legal car hybrid drive in the world. Proof of this are its 1.38 litre per 100 kilometres fuel consumption and 36 g/km CO2 emissions. Serving as the primary drive source is a completely redeveloped two-cylinder turbo-diesel with common rail direct injection (TDI). It is operated in two different modes depending on the load conditions. In the standard "ECO" mode, the 800 cm3 TDI develops a power of 20 kW / 27 PS (at 4,000 rpm); in "Sport" mode - used to reach top speed, for example - the car's power rises to 29 kW / 39 PS (at 4,000 rpm). The TDI's maximum torque is 100 Newton-meter (at 1,900 rpm). Naturally, the Volkswagen L1 also has a Stop-Start system that automatically shuts down the engine when vehicle has stopped and restarts when the accelerator or E-pedal is pressed.

The hybrid module has been integrated into the housing of the 7-speed DSG (Direct Shift Gearbox). It is located between the TDI engine and the DSG gearbox and consists of a 10 kW / 14 PS electric motor and a clutch. The E-motor is supplied with energy from a lithium-ion battery located at the front of the car. An electronic power control module, operating at around. 130 Volts manages the flow of high voltage energy the battery and to the E-motor. In parallel, the vehicle's low voltage electrical system is supplied with the necessary 12 Volts through a DC/DC converter.

Electric motor - details of the E-motor

In normal operation the electric motor can support the TDI engine in conditions such as by electronic load point shifting and in acceleration. If necessary - generally during acceleration - the E-motor can supply 40 percent additional torque over the entire speed engine speed range. Moreover, the E-motor can propel the Volkswagen L1 over short distances by itself. In this case, an auxiliary clutch decouples the TDI from the drivetrain. Restarting the TDI is a very easy process. In so-called "pulse starting" of the TDI, the electric motor is sped up and is then coupled to the TDI unit to provide almost instant starting. The entire process takes place automatically and without jolts, so the driver hardly notices the restarting of the TDI engine.

In braking phases, the E-motor operates as a generator to charge the lithium-ion battery by recovering braking energy. The gears of the automatically shifting DSG are always selected with the aim of achieving the best possible fuel economy. The engine controller regulates all energy flow and drive management tasks taking into account the moment by moment demands for power made by the driver. Some of the parameters used to calculate the optimum propulsion mode for the given conditions are: accelerator pedal position, engine load, momentary fuel demand, energy supply and the mix of kinetic and electrical energy at any given time.

Diesel engine - details of the 0.8 TDI

The TDI engine in the Volkswagen L1 Concept is a new development. Yet, even here Volkswagen has been able to exploit synergies to design an engine that is both innovative and cost-effective. Hence, this 0.8 litre TDI unit has been derived from the 1.6 TDI just introduced a few months ago. The 1.6 TDI is making its debut at the IAA in cars such as the new version of the Golf BlueMotion (3.8 l/100 km) and the Passat BlueMotion (4.4 l/100 km) - which are currently the world's most fuel-efficient production cars in their respective classes.

Based on their common origins, the 0.8 TDI and 1.6 TDI have identical cylinder spacing (88 millimetres), bore (79.5 millimetres) and stroke (80.5 millimetres). These high-tech TDI engines also share key internal engine features for reducing emissions. They include special piston crowns, multi-injection and individual orientations of the specific injection jets. On both drivetrains there is exhaust gas recirculation, an oxidation catalytic converter and a diesel particulate filter. Equipped this way, the TDIs in each Volkswagen fulfil the limits of the Euro-5 emissions standard with ease.

The 1.6 TDI, thanks to its common rail injection, is also an exceptionally quiet and low-vibration diesel engine. These positive properties have been successfully transferred to the two-cylinder unit. The TDI's aluminium crankcase was also constructed with high precision to achieve very low friction losses. The oil pump, designed to operate at a maximum oil pressure of 4.0 bar, also contributes to engine efficiency.

Another example of how the entire drive system is configured for high efficiency is the Volkswagen L1's cooling system. Its external water pump is controlled by engine management so that cooling is only activated while engine operating conditions require it. This thermal management also contributes to reduced fuel consumption. A second electric water pump, also activated only when needed, provides cooling required for the starter generator and the power electronics in a separate water circulation loop operating at a lower temperature level.

Automatic transmission - details of the 7-speed DSG

Gear shifting work aboard the Volkswagen L1 is handled by the 7-speed DSG, which is one of the most innovative automatic transmissions in production. Compared to the version equipping the new Polo, for example, the design of the Direct Shift Gearbox has been developed to include clutch control for the hybrid module. Furthermore, individual gear ratios have been optimised to attain responsive driving performance despite the car's extremely low fuel consumption. The hybrid module is integrated into the DSG housing as previously mentioned. It is located where the flywheel is usually to be found.

Driving performance - economical and yet responsive

The Volkswagen L1, equipped with ABS and ESP, has a top speed of up to 160 km/h - this is remarkable considering its fuel efficiency. With maximum acceleration from a standstill, the two-seater reaches 100 km/h after just 14.3 seconds. The fuel tank holds just ten litres yet, this is sufficient for a theoretical driving range of about 670 kilometres, given the car's 1.38 litre average fuel consumption.

Interior

Talking about car driving as 'piloting' might sound out of place, but in the case of the Volkswagen L1 it is wholly appropriate. The driver (in the CFRP tube frame seat) and passenger (in the fixed CFRP seat that is part of the monocoque) sit one behind the other. At both locations, the seat position is ergonomical and very comfortable. All instruments and controls are arranged over a 180 degree radius for the driver, which places them perfectly within view and reach. The instrument panel itself has been integrated into the monocoque and is made of CFRP. The interior applications are produced from glass fibre reinforced plastic (GFRP). One of the materials Volkswagen is introducing for interior side trim is the new "Sport Esteem" material that is as robust as it is touch-friendly.

To start the Volkswagen L1, the driver pushes a button on the right side of the steering wheel. When it is rotated, the round start button simultaneously serves as a gear selector switch and is used to activate the electronic handbrake (Drive, Neutral, Reverse and Park). The entry canopy and rear hatch are opened electrically by touch controls to the left and right of the driver. Also designed as touch sensors are controls for the entire air conditioning control system. Via multifunctional keys in the steering wheel, the driver controls the on-board computer, navigation and entertainment systems.

The classic door mirror and rear-view mirror have been completely eliminated on the Volkswagen L1. In their place, cameras display images on OLED-active (OLED = organic light emitting diode) displays located on the left and right sides of the instrument panel. A Park Distance Control (PDC) system makes parking easier as well.

In case of a crash, not only are the driver and passenger protected by the monocoque, which is designed as a highly rigid CFRP safety cell, as well as aluminium crash elements in the front of the car, but also by a steering wheel airbag and head/side curtain airbags to the left and right inside the entry canopy.

Body

Both technically and visually, the CFRP body is already a significant achievement in car design. Unique on this car: the proportions of its dimensions. While the length of the Volkswagen L1 at 3,813 millimetres is still similar to that of a Volkswagen Fox, and its height of 1,143 millimetres nearly matches that of a Lamborghini Murciélago, the car's aerodynamically optimised width (1,200 millimetres) has no comparisons in the world of today's production cars.

CFRP body - Monocoque and exterior skin

The two-seat monocoque, including the tubular frame driver's seat and passenger seat as well as the exterior body skin, all consist of CFRP. There are no doors. Instead, the driver and passenger climb into the Volkswagen L1 from the top. An electrically actuated entry canopy above the seats is opened and closed for this purpose. Headlights and taillights all utilize LED technology, which consume a lot less energy. The rear wheels are completely covered; their wheel covers can be removed to change the Michelin low resistance tires ("Energy Saver": front 95/60 R16, rear 115/70 R16). The underbody is also completely enclosed. The 0.8 TDI is cooled via adaptive air channels integrated in the sides of the car body. These automatically open and close based on the hybrid unit's operating state and vehicle speed. The tailgate is opened in the usual, manual way. It too consists of CFRP. Inside is a stowage space of 50 litres.

CFRP advantages - composition and weight

Carbon fibre reinforced plastic, as the name implies, consists of multiple layers of high-strength carbon fibres, which are integrated in a very tough matrix. This mix results in an extremely strong and lightweight composite material. Until now, producing a body like that of the Volkswagen L1 from CFRP, while conforming to industrial standards, was an insurmountable task. Up to now CFRP was only practical for very small production runs, as in aircraft manufacturing or motorsport. Now Volkswagen has succeeded in finding a production-viable and cost-effective way to produce CFRP parts in suitable volumes.

The reason that CFRP is the ideal material for the Volkswagen L1 body is demonstrated by considering its weight and strength. The Volkswagen L1 weighs just 380 kilograms, which is equivalent to the weight of a very high-end, fully equipped touring motorcycle of the 1200-cc class. The Volkswagen L1, on the other hand, is an automobile through and through. Of the 380 kilograms curb weight, 122 kilograms are taken by the drivetrain, 79 kilograms by the chassis, 35 kilograms by interior furnishings and 20 kilograms by the electrical system. 124 kilograms remain, and this is precisely the weight of the body.

These 124 kilograms can be further broken down: 64 kilograms are accounted for by the CFRP monocoque including integrated passenger seat, 28 kilograms is the weight of the entire CFRP exterior skin, 19 kilograms for the CFRP entry canopy, 9 kilograms for the CFRP driver's seat and 4 kilograms for the LED lights. By way of comparison: The body of the legendary Lupo 3L - until today the smallest Volkswagen production car ever built - weighed 306 kilograms, and the entire car weighed a lightweight 813 kilograms. That is 433 kilograms more than the Volkswagen L1.

And there are other advantages: the material's extremely high stress limits and its ideal forming properties for even the most challenging of design features.

Design - anything but typical, yet a typical Volkswagen

The design and styling of the Volkswagen L1 Concept - function and form - combine to form one uncompromising unit. Walter de Silva, Head of Design for the Volkswagen Group has this to say: "The design of the Volkswagen L1 redefines classic and aesthetic vehicle traits. Especially significant, of course, is how the nearly rocket-shaped lines catch one's attention. All of its moving parts are integrated so accurately that the body resembles a rocket or jet. It is a body that cuts through the air with minimal aerodynamic resistance." A top Cd value of 0.195 and 1.02 m2 frontal area (Cd x A = 0.199 m2) is a statement that is sculpted into the CFRP.

And this is how it looks, the most aerodynamic front end in the world: "The typical layout of conventional headlights with a radiator grille in the middle would be entirely inappropriate here," says de Silva. "That is why we chose a more minimalistic layout and integrated the headlights into a neutral horizontal stripe that conveys a far-sighted and contemporary feeling." The Head of Group Design continues: "In a sense, we applied the same principle to the front end of the Scirocco, where the headlights are joined by a glossy black stripe, and the brand logo is also placed on the engine bonnet. This underscores the dynamic character of this automobile."

The extremely aerodynamic design also shapes the rear with its diffuser and wheels that are completely enclosed. The most distinctive feature of the overall appearance in the rear are the LED taillights that were worked into the TDI's air outlet ports. De Silva: "The same stylistic features as in front are repeated in the rear, in the taillights - which we have integrated in the grilles of the two air outlet ports; they have an even more aerodynamic appearance. Another identifying feature is the air outlet directly behind the cockpit - a nearly abstract, graphic element that underscores the purposeful aesthetics of this vehicle." Due to the driver's low seating position, there is an additional window in the roof that is ideal, for example, to view traffic lights.