Ford Faced Challenges in Developing Fusion Start/Stop System

SANTA MONICA, CA – Ford engineers closely studied the stop/start systems offered by BMW and Porsche while developing a version of the technology for the all-new ’13 Ford Fusion.

“Given that stop/start has been on manual transmissions in Europe for about five years, we looked to those manufacturers as having some experience under their belt,” Birgit Sorgenfrei, Ford auto stop/startprogram manager, tells WardsAuto during a media event here.

BMW offers stop/start on a variety of models, including the 1- and 3-Series, while Porsche offers it on nearly all its models.

Sorgenfrei says Ford keeps a close eye on competitors and usually is aware of a new technology about to debut. But that was not the case with BMW, which caught the U.S. auto maker off guard when it launched its stop/start system last year.

While Ford has offered stop/start on its hybrid models for years, BMW beat it to market with a system designed for non-hybrid vehicles.

However, BMW’s stop/start was found lacking when it came to noise, vibration and harshness, Sorgenfrei says. “On NVH, we were quite surprised on (the) implementation. When our team looked at delivering stop/start, we wanted to make sure it was seamless and intuitive to the customer.”

So Sorgenfrei’s team decided to benchmark Ford’s own hybrids, which have received positive reviews for smooth restarts. “There are always those opportunities to do things a little bit differently, and we’re investigating those,” she says.

There were other hurdles in designing a stop/start system for the non-hybrid Fusion. For instance, Ford’s hybrid system benefits from having a powerful lithium-ion battery to power startups and keep other electrical systems going.

Adding to the challenge was the team’s edict to keep the cost of the new stop/start system at less than $300, which made it impossible to utilize a pricey Li-ion battery pack. Instead, engineers used an absorbed glass-mat battery.

“The chemistry is a little bit different, but the benefit is deeper cycling and supporting more loads, which we have to do on a stop/start system and cold-weather operation,” Sorgenfrei says.

With only 12V to work with, the Ford team had to be judicious in supporting all of the electrical content on the non-hybrid Fusion. The result is system-control software that includes a simulated model of the electrical system, which constantly monitors accessory loads.

The model factors in current draw by features such as headlights and climate control to predict how much power will be available with the engine off and how fast the battery will drain. If the electrical load demands too much from the battery, the stop/start system can be disabled to prevent a rough restart or depleted battery.

Sorgenfrei says stop/start places a lot of stress on the starter, which is tasked with cranking the engine five times more than is required for a car without the system.

“We did a lot of testing on our starter designs, and the implementation is still primarily conventional, where you have a pinion engaging the ring gear on the engine,” she says. “But we hardened the ring gear to make sure that it was robust enough for the increased number of stop/start cycles.”

Until recently, most non-hybrid vehicles with stop/start had manual transmissions. Because an automatic transmission must maintain internal hydraulic pressure with the engine on or off, Ford added an electrically driven pump.

In order to minimize launch delays after restart, the engineers wanted to keep the transmission in gear even with the engine off, as opposed to shifting it into neutral. “We had to develop some unique control algorithms for the engine and transmission to overcome this obstacle and still ensure a quick, smooth and quiet restart,” Sorgenfrei says.

Ford’s stop/start system is offered as a $295 option only on the ’13 Fusion equipped with a 1.6L EcoBoost engine, because it is the most fuel-efficient Fusion model.

The system improves fuel economy 3.5%, Sorgenfrei says, noting efficiency is even better under certain conditions. “Depending on driving style, real-world fuel savings can be as high as 10%.”

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