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 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 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 L1 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 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 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 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.