/*ONEIGHTURBO

Volkswagen is contributing 20 of the latest generation Golf Variant twinDRIVE 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 twinDRIVE fleet.

• twinDRIVE has potential for a great future
• Golf Variant twinDRIVE can be driven up to 57 km in pure electric modeTotal driving range of the twinDRIVE is about 900 kilometers

Electric motor is primary drive

The plug-in hybrid drive of the Golf Variant twinDRIVE differs fundamentally from hybrid systems without an external electrical charging port. First, thanks to its greater battery capacity (up to 13.2 kWh), the twinDRIVE 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 twinDRIVE – 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 optimizes load distribution between the electric and internal combustion engine drives to minimize 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 utilize the E-motor with zero emissions for the pure city kilometers of a driving route, e.g. from Leipzig to Berlin – including city kilometers 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 twinDRIVE (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 twinDRIVE 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 maximize 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 twinDRIVE can reach a respectable top speed of 120 km/h.

The Golf Variant twinDRIVE 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 twinDRIVE: 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 twinDRIVE 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 twinDRIVE 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 optimizes 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 optimize 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 analyzed 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.

- Volkswagen Group