|Introducing the twin up! Click to enlarge.|
Volkswagen presented the twin up! concept car at the Tokyo Motor Show. Equipped with a plug-in hybrid system from the super-efficient XL1 (earlier post), the four-seater based on the up! city car achieves combined fuel consumption of 1.1 liters per 100 km (214 mpgUS) (NEDC), with corresponding CO2 emissions of 27 g/km.
All new Volkswagen vehicles are configured to accept alternative drive systems as well as conventional ones, making installation of the compact XL1 plug-in hybrid system in the twin up! relatively easy. The only modification made in the production version was to lengthen the up!’s extremely short front overhang by 30 mm. The drive unit of the twin up! (system power: 55 kW) is mounted at the front of the car. It comprises a two-cylinder 0.8L TDI (35 kW); electric motor (35 kW); a 7-speed DSG (DQ200E) and the power electronics.
|From XL1 to twin up! Click to enlarge.|
The two-cylinder TDI was derived from a common rail four-cylinder (1.6-liter displacement). The 0.8-liter TDI has a cylinder spacing of 88 mm; its bore is 81.0 mm, and its stroke is 80.5 mm. Besides reduced engine displacement, other emissions-reducing measures were implemented such as specially formed piston recesses, multipoint fuel injection and controlled orientation of individual injection sprays. Smooth running of the small engine is ensured thanks to a balancer shaft. An exhaust gas recirculation system, oxidation catalytic converter and diesel particulate filter are used to reduce emissions values.
Located between the TDI and the 7-speed DSG is the hybrid module with an electric motor and decoupling clutch; this module was integrated in the DSG housing in place of the usual flywheel. The electric motor is supplied with energy from the 8.6 kWh lithium-ion battery that can be charged by the TDI. The power electronics, which operate at 308V, manage the bidirectional flow of high-voltage energy between the battery and the electric motor and convert direct current to alternating current.
The engine compartment of the twin up! is completely covered. All service access points are in maintenance-friendly locations. A matt black engine compartment cover with acoustic insulating effect organises all recognizable components, providing for better organisation. The power electronics, and the service access located across from it, are integrated in a high-gloss black band, which also functionally partitions the engine compartment. A central acoustic capsule unites design themes from the world of combustion engines and electric motors; the electric elements are coded in the color blue.
|Phantom views of the twin up! Click to enlarge.|
The two “tank systems” are located in the back, underneath the rear bench seat and the luggage compartment: the lithium-ion battery as well as a 12 V battery for the vehicle’s electrical system and a 33-liter (8.7 gallon) fuel tank.
In all-electric operation the twin up! can cover a range of 50 km (31 miles). The twin up! accelerates up to 60 km/h (37 mph) in 8.8 seconds and has an all-electric top speed of 125 km/h (78 mph). The components of the plug-in drive system give the concept car a top speed in hybrid operation of 140 km/h (87 mph) and at the same time provide a high torque for a small car of 215 N·m (159 lb-ft).
In electric mode, the TDI is decoupled from the drivetrain by opening the decoupling clutch and is shut off. Meanwhile, the driving clutch on the gearbox side remains closed, and the 7-speed DSG is fully engaged. Provided that the battery has a sufficiently high state of charge, the driver can choose when and where the twin up! should be driven all-electrically by simply pressing the e-mode button.
Later, the process of restarting the two-cylinder engine is a very smooth process. When a "pulse start" of the TDI is performed while driving, the rotor of the electric motor is revved, and the engine-side clutch is engaged very quickly. This turns the TDI, accelerating it to the necessary engine speed, and starts it.
When the twin up! is braked, the electric motor operates as a generator; its braking energy is used to charge the battery. Load point shifting of the TDI, which can be performed under certain operating conditions, has a positive effect on engine fuel efficiency, including energy usage in the hybrid system. Load point shifting makes the turbodiesel operate at more favorable efficiency levels, and excess energy can be fed to the battery.
Another method for improving fuel efficiency is in gear selection of the automatic 7-speed DSG. The engine controller regulates the entire energy and drive management system based on the specific load demanded by the driver. Parameters flowing into this control system include the accelerator or e-pedal position, engine load, energy supply and mix of kinetic and electric energy, so that the system always uses the optimal type of propulsive power.
Controls and display components were redesigned for the twin up!, and user control, status display and climate control functions on the concept car were implemented entirely in digital form.