Maybe I'm
barking up the wrong tree, but have serious difficulty believing Bosch's claim
'During the average trip, according to Bosch, around 30 per cent of the time is spent coasting'. Even going over a familiar section of road trying to replicate coasting conditions (revs/speed etc) sometimes it coasts and sometimes it doesn't, even when using tricks, e.g. lightly tapping the '+' paddle. We've done trips 400m to 4000m & lucky to get 10% coasting. Perhaps if they were '
economy runs'
, like car clubs hold, totally different scenario. On that basis the fuel economy may well be to the point where it has a significant affect, but I have difficulty in how, in the real world, Audi can convince EU authorities that any portion of the fuel economy benchmarks can be attained through coasting. Until S4/S5 TFSI's go hybridisation with the electric coasting function, coasting is only based on gravity.
This is an excerpt from the recent Audi-Media Centre release this month on the Audi S5 TDI:
'MHEV technology: recuperate or coast
The mild hybrid system in the S models, which is also integrated into the new 48-volt electrical system, has the potential to reduce customer fuel consumption by as much as 0.4 liters per
100 kilometers. Mounted on the end face of the 3.0 TDI is a water-cooled belt alternator starter (BAS), which is connected to the crankshaft via a particularly high-load poly-V belt. The BAS generates a recuperation power of up to 8 kW and 60 Nm (44.3 lb-ft) of torque. It interacts closely with the TDI engine, which in many situations can be operated more closely to its ideal load point as a result. That enhances efficiency.
When drivers take their foot off the accelerator pedal at a speed between 55 and 160 km/h (34.2 to 99.4 mph), the car can coast for up to 40 seconds with the engine shut off completely. The lithium-ion battery continues to supply electricity. The engine management system decides anew in every situation whether coasting, freewheeling or recuperation, i.e. the recovery of kinetic energy, is most efficient. It does this using information from the navigation system and the onboard sensors. The energy recovered by the BAS during coasting and braking flows into the 48-volt storage unit or directly to the electrical consumers.
* Fuel consumption and CO2 emission figures given in ranges depend on the tires/wheels used as well as the selected equipment
The mild hybrid system not only reduces fuel consumption; it also provides greater comfort and convenience. The conventional starter is only used to start the car initially, when cold engine oil requires high forces. When the driver presses the accelerator pedal again after a coasting phase or a stop, the BAS restarts the combustion engine. The system does this as required by the driver’s wishes and the situation, from very smoothly to very quickly. Start-stop operation begins at 22 km/h (13.7 mph). When stopped, the engine restarts as soon as the car in front starts to move, even if the brake is depressed."
