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Ford concentrates on control strategies for low-cost start-stop system for Fusion

The new Ford Fusion will be the first non-hybrid Ford vehicle available in the US with Auto Start-Stop. (Earlier post.) Priced at an incremental $295, Auto Start-Stop can improve real-world fuel efficiency by 3.5%, and can pay for itself in fuel savings in less than 18 months, according to the company.

In its quest to keep the system very affordable, Ford wanted to keep the supporting battery a 12V battery, but also didn’t want to compromise durability, said Birgit Sorgenfrei, Ford’s Auto Start-Stop program manager. The company focused heavily on developing control strategies not only to ensure smooth and robust restarts and driver comfort, but also to minimize the negative impacts of the start-stop duty cycle on the Advanced Glass Mat (AGM) battery. As a result, Ford engineers have more than 25 patents pending for innovations developed in the electronic control strategy for the $295 system.

One of the critical parameters for a start-stop system battery is dynamic charge acceptance (DCA). In a recently published paper with colleagues from RWTH Aachen University and Digatron Industrie-Elektronik GmbH, Eckhard Karden of Ford Research and Advanced Engineering Europe noted that:

Stop-start and regenerative braking are the hybridization features used for micro-hybrids, while avoiding the need for a high volt (above 60V) electric motor and traction battery. In it most widespread and lowest cost implementation, the topologies of a micro-hybrid vehicle’s powertrain and electric power supply system are the same as in conventional vehicles with internal combustion engine, i.e., a 14V generator with modified control algorithms and one lead-acid battery (or sometimes two) perform the brake energy recuperation.

Together with novel vehicle functions like electrically assisted brakes and steering systems, or cabin pre-heating during key-off, micro-hybridization confronts the starter battery with substantially increased energy throughput by micro-cycling with a typical amplitude (depth of discharge, DOD) around a few percent state of charge (SOC) or less. Fast recharge of the battery during these micro-cycles under a broad range of real world usage conditions, like temperature and driving profiles, is a pre-requisite for consistently high availability of stop/start and other essential functions for the customer.

It has been proposed to characterize the recharge ability of vehicle starter batteries as dynamic charge acceptance (DCA). Fuel savings due to regenerative braking critically depend on the DCA of the battery. With an appropriate modification of the alternator control strategy, lead-acid batteries can provide brake energy recuperation functionality.

—Budde-Meiwes et al.

While the energy throughput of AGM batteries is generally sufficient, DCA is an acknowledged challenge as the battery can’t handle more than a half to a third of the power the alternator can provide.

Although other approaches to lead-acid such as PbC or alternative electrochemical systems such NiZn can offer weight reduction, promise longer service life and better charge acceptance, there are as yet unproven at volume and over time, and system integration into 14 V power supply systems could pose a challenge, Ford says.

AGM batteries are actually a very good solution for start/stop. They are used extensively throughout European applications. It is a more durable 12V lead-acid battery. It has been proven in bench testing as well as being able to deliver on the target.

Many of the patents associated with [the Fusion start/stop system] make sure that the system recognizes the battery capability and works to those. The power of our system is that the controls that are used to determine if the engine shuts down or is started take into account the battery, both in terms of short term charge availability as well as in terms of lifetime. We want to make sure that both are maintained in a healthy zone.

We look at what kind of current draw is being used in the vehicle, the powertrain controller makes the decision based on those measurements to ensure that the battery remains healthy.

—Birgit Sorgenfrei

The Ford system. Until now, most non-hybrid vehicles with Auto Start-Stop have only been available with manual transmissions, but US drivers overwhelmingly opt for automatic transmissions. The new Fusion is the first Ford vehicle to offer Auto Start-Stop with a self-shifting gearbox. Since an automatic transmission needs to maintain internal hydraulic pressure even with the engine off, Ford added an electrically driven pump to the transmission along with the upgraded starter motor and the absorbed glass mat battery.

In order to minimize launch delays after a restart, the engineers wanted to keep the transmission in gear even with the engine off as opposed to shifting it into neutral. This required some unique control algorithms for the engine and transmission, Sorgenfrei said.

The control software includes a simulation model of the electrical system that constantly monitors the accessory loads. The model factors in the current draw from features like headlights, climate control, audio system and window defoggers to predict how much power will be available with the engine off and how fast the battery will drain. If the electrical load is demanding too much from the battery, Auto Start-Stop may be disabled to prevent a rough restart or being stuck with a flat battery.

Voltage blending is another technology Ford is seeking to patent. While the engine is running, the alternator produces about 14 to 15 volts, but the battery only produces 12 volts with a full charge. When the Fusion is slowing down with Auto Start-Stop enabled, the load model tracks the vehicle speed and deceleration and then calculates when to ramp down the voltage from the alternator to the battery-only level before the Fusion stops. This blending helps to ensure the driver doesn’t experience any light dimming or sudden fluctuations in ventilation fan speed.

The Auto Start-Stop team has also filed several patent applications related to the signal monitoring and controls for the climate control system. In addition to the cabin temperature and humidity, Auto Start-Stop monitors the temperature of the evaporator core that starts to rise before the occupants even feel a change inside the car. When this happens, the engine will restart sooner.

The 2013 Fusion with Auto Start-Stop also provides coaching to the driver.

When Auto Start-Stop is disabled because of a high accessory load, we wanted drivers to understand why so that they could opt to switch some things off if it’s appropriate. If the rear defrost is still on but the window is clear, they can switch it off to gain the efficiency benefit of shutting down the engine when the car stops.Auto Start-Stop engineering supervisor Kirk Pebley


  • Heide Budde-Meiwes, Dominik Schulte, Julia Kowal, Dirk Uwe Sauer, Ralf Hecke, Eckhard Karden (2012) Dynamic charge acceptance of lead–acid batteries: Comparison of methods for conditioning and testing, Journal of Power Sources, Volume 207, Pages 30-36 doi: 10.1016/j.jpowsour.2011.12.045



If the EPA allows Ford to include an off-switch most drivers will just turn it off.. its irritating to hear the starter cranking the engine every time you stop for a light. GM's eAssist is silent because it uses a belt to drive the engine.


Peugeot's system using Maxwell ultracapacitors seems far more robust to me, with the capacitors good for around 600,000 stop/start events.


How can someone get 26 patents on something that has been in full time operation in a few million vehicles for about 10 years? Did all others forget to apply for patent rights?


When you've got a scheme that works with a cheaper battery technology, you're doing something novel and you can patent it.

If the payoff is just 18 months, Ford may be able to get some money from license fees as well.


E-P...what happened if many others are already doing it? Will we have an Apple/Samsung style international law suit?


PowerGenix has licensed their NiZn battery tech to be built in China by the end of the year. I expect many OEMs to use this battery for micohybrids in the has too many pluses to be ignored, i.e., higher voltage, faster DCA, a higher discharge C rate, a 30% lighter battery for the same AmpHour rating, and it is non-toxic to re-cycle. It will be a much better chemistry than Pb AGM batteries all around as long as it not too expensive.


Who's doing it with PbSO4 AGM cells?

The inventions appear to be specific to the cell type, and permit the use of a cheaper battery.  Nobody else is likely to have solved the same problems, so there should be no conflict of patents.  On the other hand, a patent on an invention which yields a cost advantage is something that can be turned into money through licensing.


And you cannot patent something after it is on sale or in public use in the United States more than one year - even if you invented it.

A Yahoo! user

Davemart, Yeah but the Peugeot system couples the Maxwell ultracaps with one of those bad lead acid batteries. Just no getting around those hotel loads and the need for the efficient application of capital in the private sector.


Roger Pham

In most locations in the USA, summers are hot necessitating A/C while winters are cold, necessitating heater. These requires that the engine be kept running in cars with just stop-start option, thus significantly reduces the utility of this device, and I suspect that the fuel-efficiency gain may be less than 3.5% in those areas.

A full hybrid has electric A/C compressor and coolant storage of engine heat to allow the engine to be shut down at stoplights even in cold winters and hot summers. A Ford Fusion at 27mpg burns $25,900 worth of gasoline in 200,000 miles, while the 2013 Fusion Hybrid at 46mpg will burn $15,200 worth of gasoline in 200,000 miles, for a net saving of 10,700 dollars. The hybrid version will save even more money on lack of brake service and transmission service or replacement, thus will up the saving to may be in the $15,000 range. The price premium for the hybrid version is only about ~5,000 higher than an equivalent non-hybrid version. U can save as much as $10,000 by going with the Fusion Hybrid. The new Lexus hybrid markup for the Eh-300 is only $2,700 more than a non-hybrid version, allowing even more savings.
If one wants to save money and save the planet, why not go all the way?

Roger Pham

I must hasten to add that the savings in fuel costs are calculated for gasoline at $3.50/gallon. Higher fuel prices in the future will net you even more savings. U can go all the way!


You can still use stop-start in cold weather; all you need is an electric pump to circulate coolant through the heater core while the engine is off.  If worse comes to worst, you can store some heat in a phase-change material.


Electric vehicles/cars should have improved cabs to reduce heating/cooling needs. Currently, a small 100 cu.ft. cab needs almost as much heating/cooling energy than a small well build apartment with 60+ times the volume. Insulating the cab from hot sun and cold winds is a very well known technology. Instead of moving in that direction, many have increased the size of the useless glass sun roof, making matters worse.

Heated seats and one or two people should generate enough heat to keep a well made 100 warm. A small ethanol heater would be added for emergencies.


You should give some thought to the phrase "Priced at an incremental $295."

And that $295 is the incremental PRICE; there is labor, overhead and profit in there.

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