The MQB strategy of the Volkswagen Group extends from the A0 to the C-segment. There is some overlap at the low-end with the NSF and in larger vehicles with the MLB. Click to enlarge.

The modular toolkit approach, in this case the MQB, also offers flexibility. For example, the CrossBlue Coupé plug-in hybrid sporty mid-size SUV show car, introduced at Auto Shanghai 2013, is also based off the MQB architecture, but featured a transverse-mounted turbocharged direct-injection (TSI) 220 kW (295 hp) 3.0L V6 gasoline engine (EA 390) and six-speed DSG dual-clutch automatic transmission with 40 kW electric motor as part of the DQ400E hybrid module in the engine compartment, rather than the 1.4-liter engine and 80 kW motor DQ400E in the A3 e-tron and Golf GTE plug-in hybrids. (Earlier post.)

Example of an MQB plug-in hybrid powertrain. While the electric motor and battery pack are the same size as spec’d for the A3 e-tron and the Golf GTE, the combustion engine (VB) is at a lower power rating. Click to enlarge.

The Volkswagen Group has said the Audi A3 e-tron will come to the North American market in 2015; introduction plans and timing for the Golf GTE are as yet unspecified. However, given their lineage (the A3 and Golf), the vehicles will be key components of the Group’s broader—and aggressive—electrification strategy, enabled and accelerated by the MQB and its cousins.

As one example, an MQB-based Passat plug-in hybrid will join the line-up “soon,” according to Volkswagen Group Chairman of the Board of Management Prof. Dr. Winterkorn in remarks prior to the Geneva Motor Show in March. (Earlier post.)

From a 2013 Volkswagen Group presentation. Click to enlarge.

The Golf GTE and Audi A3 e-tron. The plug-in hybrid drivetrain is designed as a parallel hybrid system. The basic main components common to both the Golf GTE and the A3 e-tron are:

• a 4-cylinder, 1.4-liter TSI gasoline engine from the EA 211 series (which spans 1.0L to 1.6L displacement);

• the DQ400E dual-clutch gearbox (combining the electric motor, engine-disconnect clutch and base gearbox into a highly integrated, compact unit);

• the 80 kW liquid-cooled electric motor (HEM80), integrated into the DQ400E; and

• a liquid-cooled 8.8 kWh Li-ion battery pack (about ~7.0 kWh usable).

The brake system uses an electromechanical brake booster (eBKV, elektromechanische Bremskraftverstärker). It divides the required deceleration power according to demand between the electrical and hydraulic systems, and enables a high degree of recuperation. (The system is also being developed for application in non-hybrid applications.)

All-electric range is projected to be up to 50 km (31 miles); on a 2/3 all-electric and 1/3 hybrid route, the Audi and Golf are expected to deliver an average NEDC fuel consumption of 1.5 l/100 km (157 mpg US), or 35 g/km of CO₂.

DQ400E. The DQ400E will be the Group’s main near-term gearbox for all hybrid and plug-in hybrid applications that are transverse, noted Oliver Schmidt, General Manager Engineering and Environmental Office, Volkswagen Group of America, at the SAE 2013 Hybrid & Electric Vehicle Technologies Symposium. (Earlier post.)

The friction-optimized unit, with six forward gears, features oil supply on demand, two-circuit hydraulic control (high and low pressure, 40 bar and 5 bar) and a highly efficient synchronizer system. The power flux is divided across two component gearboxes using a coaxially split drive shaft with an upstream drive clutch for each. The wheel set is of a highly compact design to make space for the electric motor.

The DQ400E system is equipped with two drive clutches (K1/K2) and the engine-disconnect clutch (K0). The drive clutches are each designed for maximum input torques of 400 N·m (295 lb-ft); the engine-disconnect clutch for 350 N·m (258 lb-ft).

The engine-disconnect clutch actuation unit is installed in the clutch chamber between the rotor arm of the electric motor and the input shaft; the rotor arm is a component element of the electric motor and of the drive clutches.

HEM80 motor. Click to enlarge.		The DQ400E transmission. Click to enlarge.

HEM80 electric motor. The 80 kW, 330 N·m (243 lb-ft) three-phase permanently excited synchronous machine is located in the hybrid module on the input shaft, between the engine-disconnect clutch and the drive clutches (K1/K2). It is integrated into the vehicle’s on-board cooling system.

The rotor and stator are made of punched electric sheet steel. The rotor integrates the permanent magnets, while the stator incorporates the three-phase copper windings. Sensors detect the rotor position, providing an input variable for control of the phase currents through the power electronics.

Li-ion battery. The Li-ion battery pack comprises eight modules, each made up of 12 prismatic nickel-manganese-cobalt cells. The Battery Junction Box (BJB) and the Battery Management Controller (BMC) are integrated into the die-cast aluminium and plastic battery casing. Voltage is between 250 and 400 V depending on state of charge.

Thermal management. The plug-in hybrid uses a three-circuit cooling system: one high-temperature circuit and two low-temperature circuits.

The high-temperature circuit handles the engine; the integrated gearbox oil cooler can be shut off on the water side, enabling the gearbox to be both heated and cooled. In electric driving mode the interior is heated by the high-voltage auxiliary heater (PTC). Heat sinks (cold gearbox, cold combustion engine) can be disabled in EV mode by means of bypass lines to provide rapid system response and high levels of air-conditioning comfort.

Low-temperature (LT) circuit 1 conditions components with an average operating temperature of 75 to 90 °C, such as the charge air cooler of the engine and the electric motor. LT circuit 2 handles power electronics, charger and high-voltage battery; these three components can be cooled according to demand, both passively by the LT cooler and actively via the air-conditioning circuit, which is connected to the LT circuit 2 via a chiller. LT circuit 2 can additionally be divided into two sub-circuits, enabling different temperature requirements of the various components to be met.

Drive management and operating modes. The hybrid operating strategy and drive management functions are also incorporated within the MQB. Aspects of this include:

• An engine restart request is determined by the operating strategy in the engine control unit and transmitted to the gearbox control unit. During the start sequence, the DQ400E coordinates the torques of the electric motor and the combustion engine, with the corresponding slip control of the wheel torque-dictating dual clutch (K1/K2).

  The receiving torque of the engine-disconnect clutch (K0) is balanced by a compensation torque of the electric motor so that the wheel torque remains constant. After fuel injection and ignition is enabled, the engine-disconnect clutch is re-opened; the combustion engine runs virtually load-free. Its speed is balanced to that of the electric motor by way of a torque request.

  Once the two components are synchronized, the engine-disconnect clutch is closed. After starting, the torque coordination is returned to the engine control unit.

• The catalytic converter is heated with the engine-disconnect clutch opened, and therefore independently of the driving profile. In the process, the combustion engine is run under no load at any adjustable speed level; torque is provided by the electric motor.

• Plug-in hybrid systems can run for very long periods without the combustion engine being active. Long off-times necessitate intermittent refilling of the engine oil gallery. For this, the engine is briefly turned over in order to provide a component-protecting minimum lubrication.

• The plug-in operating modes include EV mode; hybrid hold mode; hybrid automatic mode; hybrid charge mode; and sport mode.

  In EV mode, maximum speed is 130 km/h (81 mph).

  In hybrid hold mode, the state of charge of the high-voltage battery is held at a constant average value (charge sustaining). The vehicle behaves like a full hybrid, utilizing approximately 1/8 of the capacity of the high-voltage battery for maximum efficiency.

  Hybrid automatic mode is based, among others factors, on predictive route data, in order to optimize the consumption of electric power until the next charging station. This mode also provides for moderate recharging.

  In hybrid charge mode, the high-voltage battery is charged during driving by the combustion engine.

  In sport mode, full drive performance is available with the combustion engine and the electric motor. By continuously recharging to an increased average SOC, the operating strategy guarantees maximum boost performance in this mode. A slightly increased thrust torque enhances sporty performance.

Resources

• Hanno Jelden, Kai Philipp, Norbert Weiss, Andreas Kessler (2014) “Der Plug-In Hybrid Des Modularen Querbaukastens Von Volkswagen,” MTZ - Motortechnische Zeitschrift Volume 75, Issue 4, pp 40-47 doi: 10.1007/s35146-014-0315-7