Volkswagen unveils latest Golf Twin Drive plug-in hybrid prototype

Volkswagen supplies the innovative hardware in the Golf Variant twïnDRIVE

Wolfsburg / Berlin, 28 June 2011 – Today, Volkswagen – in cooperation with 6 project partners and the German Ministry of the Environment – is presenting the current status of the “Fleet study in electric mobility” that was initiated in July 2008. The primary goal of the project which runs until June 2012: consistently utilise renewable energy sources for electrically powered vehicles. Within the framework of the fleet study, Volkswagen is implementing a total of 20 of the latest generation Golf Variant twïnDRIVE cars as research vehicles. Their plug-in hybrid drives operate with zero emissions in urban operation using an electric motor. The Golf Variant twïnDRIVE enables distances of up to 57 km on pure electrical power; an additional small internal combustion engine provides for a total range of about 900 km. Prof. Dr. Martin Winterkorn, Chairman of the Management Board of Volkswagen AG, comments on the twïnDRIVE: “When it comes to driving with zero emissions within cities while covering far greater distances as pure electric vehicles – the twïnDRIVE system by Volkswagen sets new standards and could over the mid-term develop into the ideal form of mobility for the vast majority of car drivers.”

Fleet study encounters transition in energy production

The “Fleet study in electric mobility” is now assuming a high level of importance, in the wake of events in Japan and the German federal government’s mandatory exit from nuclear energy production. According to plans by the federal government, the number of pure electric vehicles will reach one million units in Germany alone by 2020. And these vehicles must be operated sustainably – i.e. from renewable energy sources – to attain significant progress in environmental protection.

Volkswagen counting on renewable energies

Before the transition in energy policy, Volkswagen had already appealed for the intensified use of renewable energy sources. During a workshop on electric mobility in Shanghai in mid-2010, Prof. Dr. Martin Winterkorn emphasised that: “Future electric cars offer us tremendous opportunities for reshaping mobility to become even more sustainable. However, we must – on behalf of the environment – ensure that the energy used to operate these electric cars is also generated renewably, i.e. from renewable resources. Since carmakers do not make decisions on which types of power plants will be built, governments must assure that environmentally-friendly energy sources are utilised. Only then will we experience a genuine transition to a new era.” This new era is now within reach.

Optimising the stability of the power grid

Over 16 per cent of Germany’s electrical needs are already covered by renewable energy sources, and plans are afoot to extend this share to 30 per cent by 2020. Volkswagen, for example, has installed one of the highest performance wind power systems in the world at its German plant in Emden; it already supplies one-third of the factory’s energy requirements. In parallel, more and more electricity is being generated from solar and water power. These forms of energy must also be used for mobility. However, the amount of renewably generated energy is subject to fluctuations due to natural factors (e.g. sunshine duration, wind strength). This means that it is necessary to intelligently control electrical demand to avoid load peaks. In this context, the “Fleet study in electric mobility” is analysing the usage behaviour of drivers of cars with electrical charging, electric load control and intelligent strategies in the charging process. In addition, a scenario is being tested, in which some of the daily peak electrical demand might be buffered by the cars’ lithium-ion batteries in the future.

Plug-in hybrid will assume much greater importance

Through its “Fleet study in electric mobility”, Volkswagen is acquiring valuable knowledge on how cars with plug-in hybrid drives like the Golf Variant twïnDRIVE handle continual use. As already noted, the 20 Golf Variant twïnDRIVE cars can be driven over long distances in pure electric mode, i.e. with zero emissions. The expression “environmental zone” takes on an entirely new meaning in cities.

One of the goals of Volkswagen AG is to launch numerous plug-in hybrid cars on the market in the years 2013/2014. In the area of electric mobility, they are intended to supplement the Group’s hybrid models that are already being produced today (these models currently include cars by Audi, Porsche and Volkswagen), as well as the pure electric vehicles that will also debut from 2013. Clearly, plug-in hybrid models – i.e. cars with combustion engine, E-motor and a battery that can be charged by an external power source – will acquire special significance in the urban environment. Prof. Dr. Martin Winterkorn comments on this: “Over the mid-term, the plug-in hybrid offers great potential here, because it unites the best of 2 worlds in one vehicle.” The plug-in hybrid, according to Winterkorn, enables precisely what many customers expect: an unlimited driving range with internal combustion engine mobility and an attractive electrical driving range in everyday driving.

Fleet study brings together specialists in Germany

The large-scale introduction of plug-in hybrid cars and pure electric cars continues to be associated with great challenges. Prof. Dr. Winterkorn: “Electric mobility will be a century-long endeavour for Europe as a centre of automotive production and industry. Carmakers, suppliers, energy providers, scientists and politicians – everyone must step up to the plate.” In Germany, the “Fleet study in electric mobility” is bringing together precisely these partners.

6 project partners

The “Fleet study in electric mobility” is being conducted by 6 project partners from research and commerce under the leadership of Volkswagen AG. Representing the energy industry is energy provider E.ON. From the research area, the Fraunhofer Gesellschaft ISIT (representation of the battery systems and development of new battery chemistry), Heidelberger Institute for Energy and Environmental Research (IFEU; creating eco-balance), the German Aerospace Centre (DLR; analysis, forecasting traffic scenarios) and the Westphalian Wilhelm University in Münster (development of methodologies, laboratory testing of battery cells) will contribute their expertise and know-how to the fleet study.

Golf Variant twïnDRIVE

twïnDRIVE has potential for a great future

Golf Variant twïnDRIVE can be driven up to 57 km in pure electric modeTotal driving range of the twïnDRIVE is about 900 kilometres

Volkswagen is contributing 20 of the latest generation Golf Variant twïnDRIVE cars to the “Fleet study in electric mobility”. In addition, 8 other Golf Variants with conventional drives are also included in the fleet study; one reason is to provide a reference point against which to compare fuel consumption values of the twïnDRIVE fleet.

Electric motor is primary drive

The plug-in hybrid drive of the Golf Variant twïnDRIVE differs fundamentally from hybrid systems without an external electrical charging port. First, thanks to its greater battery capacity (up to 13.2 kWh), the twïnDRIVE powertrain enables long driving ranges in electric mode, especially in urban driving (up to 57 km). Second, while the E-motor supplements the internal combustion engine in a hybrid model without plug-in, the setup is exactly the opposite in the Golf Variant twïnDRIVE – here, a petrol engine supplements the E-motor.

Especially in city driving and on short trips, the E-motor acts as the Golf’s primary drive unit with a power range extending up to 65 kW / 88 PS. With higher power demands, the internal combustion engine can be started to enhance vehicle performance.

The petrol engine is also used to support the electric heating system when outdoor temperatures are low.

Over mid- to long-range drives, an intelligent hybrid management system automatically optimises load distribution between the electric and internal combustion engine drives to minimise fuel consumption. In this process, the vehicle’s control system always selects the optimal operating mode –individually tailored to the current route and situation – which represents the most energy-efficient combination of electric motor and combustion engine. It should be noted that, if necessary, the driver can manually activate the pure electric driving mode (E-MODE), e.g. to drive with zero emissions in the city – provided that the battery has sufficient charge. In phases of battery regeneration (during braking) or coasting (with anticipatory deceleration), only the E-motor is active; drag torque losses are reduced by disengaging the petrol engine via a separation clutch. The results: less energy is consumed during E-mode driving; when the accelerator pedal is released, the Golf Variant “coasts” significantly longer and further.

Under certain driving conditions, the maximum driving range of 57 km noted in the introduction is possible in E-mode; when the driving range of the petrol engine is added, this increases the total range to about 900 km. Thanks to the car’s clever energy management and its innovative user input method via the radio-navigation system, the driver could program the car to utilise the E-motor with zero emissions for the pure city kilometres of a driving route, e.g. from Leipzig to Berlin – including city kilometres at the destination! In this case, the driver “reserves” an electric driving range, which is preserved in the battery, so that pure electric driving is possible whenever the E-MODE button is pressed.

Specifics of the drive system

The electric motor outputs 85 kW and supplies a strong 600 Nm of torque from standstill. When combined with the TSI engine that is currently used in the latest generation of the Golf Variant twïnDRIVE (charged petrol direction-injection engine, which also outputs 85 kW / 115 PS), a peak power of up to 120 kW / 163 PS is produced with powerful acceleration.

The entire drive unit of the Golf Variant twïnDRIVE is housed in the engine compartment; it consists of the fuel-efficient 1.4 TSI, generator (30 kW / 250 Nm), E-motor, electrically actuated separation clutch between the TSI and the E-motor as well as a 1-speed transmission. The flow of electrical energy is regulated by a high-voltage power distribution unit, which – like the battery – is located at the rear of the Golf Variant. In addition, a DC/DC converter is used to supply the 12V onboard electrical system with its required voltage.

Extremely energy-efficient network of technologies

As mentioned, this network of technologies is extremely energy-efficient. Based on guidelines for determining the fuel consumption of plug-in hybrids, a fuel consumption value of 2.1 l/100 km is attained (equivalent to 49 g/km CO2). When the battery is fully charged, the strategy is to maximise the share of pure electrical energy used for driving. Only when longer distances are driven does the share of supplemental petrol fuel increase. As a result, fuel consumption values lie well below those of conventional vehicles for most drives.

In this type of driving, the spacious and versatile Volkswagen is a very agile sort of car: its top speed is 170 km/h; the Volkswagen handles the sprint to 100 km/h in under 12 seconds. By the way, when it is operated in pure electric mode, the Golf Variant twïnDRIVE can reach a respectable top speed of 120 km/h.

The Golf Variant twïnDRIVE has 3 primary operating modes, each of which is automatically set according to the driving situation and the battery’s charge state.

Electric driving (E-drive): The car is powered exclusively by the E-motor that is supplied by the battery. The TSI is off, and the separation clutch is open. Up to 65 kW of power is available, which leaves hardly any wishes unfulfilled in normal everyday driving. The internal combustion engine can be started whenever it is needed to provide additional drive power via the generator or to charge the battery.

Driving with coupled internal combustion engine (E-motor plus TSI drive): When the TSI engine is used for driving at speeds above 50 km/h, the separation clutch closes, and the TSI is directly coupled to the drivetrain. This also enables efficient driving with pure internal combustion energy transmission at high speeds in long-distance operation. When powerful acceleration is required, the battery-powered E-motor and the TSI work together in the Golf Variant (“boosting”). Whenever necessary, the battery can also be charged via the generator.

Battery regeneration (E-motor active): When the car is braked, the E-motor – in this case acting as a generator – converts the car’s kinetic energy into electricity that is used to charge the battery. The TSI is off, and the separation clutch is open; this also applies to anticipatory “coasting”.

The 3 primary operating modes reflect the basic idea of the Golf Variant twïnDRIVE: on short drives, e.g. in the city, it is a pure electric car; on long drives, on the other hand, it is an efficient parallel hybrid.

2 battery systems for the twïnDRIVE fleet

When it comes to the car’s plug-in hybrid technology, Volkswagen is studying two different lithium-ion battery systems for the Golf Variant (Golf Generation VI). A total of 10 vehicles are equipped with batteries from the American-German manufacturer GAIA (cathode type NCA). 10 more vehicles are powered by lithium-ion batteries (cathode type NMC) from the Korean-German joint venture SB LiMotive (Samsung and Bosch); these 10 vehicles have been in use since early this year. Both battery systems offer high power and energy density. They each weigh about 150 kg.

The GAIA battery (voltage 302 V, nominal capacity 37 Ah per cell) consists of 86 cells and offers an energy capacity of 11.2 kWh. The battery from SB LiMotive (315 V, 42 Ah) with its 84 cells supplies 13.2 kWh of energy. A different class of batteries: the Golf blue-e-motion concept car with full electric drive has a battery capacity of 26.5 kWh, while the Touareg Hybrid battery stores 1.7 kWh. Cooling of the twïnDRIVE batteries is performed by the Battery Management and Monitoring System (BMS), which was developed by Volkswagen for vehicles with the SB LiMotive battery.

Clever use of batteries to supply the power grid

An innovative charge management strategy can be implemented via “intelligent” charging stations that can be operated bidirectionally. The vehicle optimises the time point of battery charging based on driver inputs (such as “Start time of next drive” and “Desired electric driving range”). These parameters are input via the radio-navigation system. By exchanging data with the electrical energy provider, the Charging Manager can optimise the charging process based on predictive tables, so that battery is charged cost-effectively and with electricity generated from renewable sources. It is even possible to feed electricity back into the electrical grid; in this type of discharging, acting as a small component of a large network, the car is essentially used as a module that helps to temporarily offset fluctuations in the electrical grid. In this case, the system operates with AC power (AC, 230 V, 3 kW).

Stations with a pure charging functionality also operate with AC power, e.g. a household electrical outlet in the garage. Charging with AC power takes a maximum of 5 hours. The third option is to charge the battery very quickly using an off-board charger with DC power (DC, 230 to 400 V, 30 kW). The charging time in this case: 20 minutes. All 3 charging modes are being studied and analysed within the framework of the fleet study.

Data logging and saving

When it comes to analysis, a wide range of data is saved. During the drive, data is continually recorded by a data logger (Car-PC) integrated in the Golf Variant. The data is transmitted to an online server via a UMTS mobile radio connection together with geo-coding of GPS position. Volkswagen Research then preconditions the acquired data to make it accessible to project partners.