Although the 1.6-liter, four cylinder EcoBoost engine that is being installed in the 2013 Ford Fusion is an efficient powertrain in and of itself, Ford engineers have set about to increase fuel efficiency by an estimated 3.5% through the use of an Auto Start-Stop system, an option that, Birgit Sorgenfrei, Ford Auto Start-Stop program manager explains, is being made available for just $295. When we talk, the EPA testing was not completed, “But based on the model work we have done, we think this is what will be achieved.”
One notable aspect of this—beside the low cost of the option to the customer—is that this is being made available in a car with a six-speed automatic transmission. Heretofore, Sorgenfrei explains, Ford’s implementation, in European vehicles, has been with manual transmission, or in hybrid vehicles. For the hybrids, the powertrain setup—with its planetary gear set and traction motors—is entirely different than that in a car with an internal combustion engine. And as for the manual transmission, she points out that “The driver has so much more involvement in controlling how the vehicle operates that it is easier to implement on a car with a manual transmission—you don’t need as much hardware or control strategy because the driver is doing some of that.” She points out, “We’ve built off of the lessons learned and the strategies we’ve developed and applied them to this vehicle.”
With the system, when the car comes to a stop—say at a light—the engine shuts off, then restarts when the driver lifts from the brake pedal. Sorgenfrei says that having a direct-injection engine facilitates the restart. To make this whole exercise seamless, the Ford engineers had to develop some unique control algorithms for the engine and transmission because they wanted to keep the transmission in gear even with the engine off, as opposed to putting the transmission into neutral. Of course, because the operation of the engine is what ordinarily provides the internal hydraulic pressure within a transmission, and because the engine is off, supplementing those algorithms is an electrically driven pump that operates when the engine is off. “We don’t want to lose the pressure,” she says.
That pump, as well as the various peripherals that are part and parcel of a car like the audio, lights, wipers, etc., are supported by a 12-volt battery. “We had to make sure that they operate without interruption,” which means that they had to develop control software that monitors the energy draw so that if the power demands are greater than that which can be handled by the 12-v battery without light dimming or fan speeds going down or the restarting being rough, the engine will be restarted even though the driver may still have the brake pedal depressed.
“We don’t have electric air conditioning in this vehicle,” she says, “so if we measure that the cabin temperature is going to exceed the customer’s climate setting, we will command the engine on to power the AC compressor.” And when it comes to heating the cabin, there is an additional water pump that circulates the engine coolant so that the heat from the engine block can be pulled off and directed to the cabin.
Sorgenfrei explains that in develop-ing the system they used data from black boxes installed in consumer vehicles as well as through performing modeling. They wanted to determine how often there would be start events and the amount of time that vehicles in the U.S. are typically stopped by traffic signals. (“The car will remain off for up to two minutes,” she says, noting that that is sufficient for about 95% of all stop lights.) This information was important because they want to make sure that the system is reliable. This has led to the use of a heavy-duty starter and an absorbed glass mat battery in place of the conventional lead-acid battery. (The absorbed glass mat battery is more durable, particularly as related to deep cycling and cold-weather operations.) “On the engine side of things,” Sorgenfrei says, “there is a hardened ring gear to deal with the increased number of start events.”
What’s the number of expected start events? Sorgenfrei says that they’ve calculated that number, which led to the design of the system—hardware as well as software—and consequently this is something that they’re not revealing. (They’ve applied for more than 25 patents for this system.)
“As an electrical team, Sorgenfrei says, “we continue to look for opportunities to optimize the use of the available energy in a vehicle.”