Published September 25, 2012
By Jeff Cobb
Not reliant on a traction motor, whether you consider Audi's "coasting hybrid" a true hybrid is up to you. Sophisticated software and control algorithms let the engine automatically turn itself off and back on again, or merely drop to idle to save fuel while the car is in motion. Whether using gravity and momentum proves more cost effective than forms of hybrids utilizing electric traction motors remains to be seen.
We’ve heard U.S. and European efficiency mandates will force automakers to develop new technologies over the next decade and beyond, while we’ve also heard “the internal combustion engine will continue to assume primary importance in the automobile for a long time.”
While many industry observers have said this of traditional engines, the above quote comes from Audi which is working on a next evolutionary step for "future" internal combustion solutions beyond stop-start system called iHEV along with complementary fuel-saving technologies.
This Intelligent Hybrid Vehicle system, as its maker calls it, goes beyond shutting off an engine to save fuel at a stop as is the case with stop-start systems, and allows a conventional petrol engine to either idle or shut off completely while the car is coasting to reduce or eliminate fuel usage.
The effect would be very much the same if you were driving down a grade or even a level section, and realizing you had enough kinetic energy to keep coasting, you briefly put the car in neutral, switched off the key and let gravity do the work. While that practice is not at all recommended, Audi is developing software and controls to automatically allow a car to safely and reliably do something akin to this and more.
Audi’s A7 Sportback 3.0 TFSI iHEV has been used to demonstrate the system which relies on an unconventional 48-volt electrical system incorporating a powerful starter motor and high-cycle-strength 48-volt lithium-ion battery located in the trunk.
The potentially networked system is very intelligent and takes myriad data into consideration to generate a seamless driving experience, according to Autocar, which briefly tested the system.
iHEV works in conjunction with Audi’s PEA (Predictive Efficiency Assistant) which takes info from the navigation system such as local speed limits, road gradient data, info from road signs and predicts what’s coming as it communicates to the driver fuel saving driving suggestions.
When the driver takes the suggestion to step off the accelerator, the iHEV system may then turn off the engine for the duration in which its power input is not needed. One example of when this could be done is when coming to a reduced speed zone in which the car could coast down. The system takes into account data such as tire and aerodynamic rolling resistance, the car’s speed and road gradient to make anyone into the ultimate hypermiler.
Even if a vehicle were to tow a trailer or add on a roof-top box, extra drag could be calculated into the system now under development.
Another technological helper is Active Cruise Control which could be used with PEA. Audi says the car can take over throttle and brake controls, and the iHEV system could turn off the engine or brake as needed to maximize efficiency.
In an interview with Autocar, Audi said with the engine idled, the A7 could coast further than 0.62 miles (1 km) when traveling on a level grade.
Audi’s press release on this and other "future engines" says the A7 Sportback 3.0 TFSI iHEV has completed a 61 km (37.90 mile) stretch of winding country roads north of Ingolstadt, with a normal, everyday style of driving and returned impressive results.
With the PEA system turned off, the driver covered 28 percent of the route with the engine switched off. Once the PEA system was activated, this figure rose to 43 percent; at the same time, fuel consumption dropped by around 10 percent, yet Audi says the driving time increased by only two minutes (three percent).