LIVONIA, MI – Stop/start systems, popular in Europe but still struggling to secure a beachhead in the U.S., are gaining sophistication as auto makers look to squeeze out every last mile per gallon while appeasing customer demands for more seamless operation.

Auto makers say North American installations of current-generation systems so far have been held down by an unfavorable Environmental Protection Agency test cycle that limits their impact on mileage ratings, making the extra cost of the devices a tough sell to American consumers.

Further restricting U.S. acceptance is performance. Operation can be crude in some applications, with engines rudely shaking back to life as traffic lights turn green and conventional starter motors crank up once the driver releases the brake or selects a gear.

But suppliers now are moving forward with development of a second wave of technology that promises to shut down engines more frequently and fire them back up faster and more smoothly to maximize fuel efficiency.

Germany’s Bosch told WardsAuto in September it will have such a system on the market in Europe in 2015-2016, with U.S. availability a year later, saying fuel savings could be as high as 15%.

Hella, which helped develop the stop/start system now going into the Ford Fusion, also has begun talking about its next-gen design that will offer a coast-down feature that cuts the engine during deceleration.

And French supplier Valeo has an advanced system onboard engineering firm Ricardo’s HyBoost test vehicle that more intelligently manages stops and starts while also supplying a short burst of electrical power at launch.

Now, U.K.-based Controlled Power Technologies, formed out of a 2007 management-led buyout of a Visteon operation in Essex, says its SpeedStart system will be ready for application in production vehicles in 2015, with an even-more advanced “micro-mild” hybrid version in the works for release later in the decade.

SpeedStart is a belt-driven, integrated starter/generator system that incorporates its own power electronics in a single package. Billed as a world first, it uses liquid-cooled switched-reluctance motors CPT says are infinitely more controllable than popular permanent-magnet motors.

Like the Hella device, the CPT system would shut off the engine during coast-down and restart it instantly when the accelerator is pressed (taking just 400 milliseconds, a speed a conventional starter motor can’t match).

The reaction time means even if a driver lifts off the throttle momentarily, the stop-start transitions will be quick, sure and smooth enough not to be an annoyance, CPT CEO Nick Pascoe promises.

“If you have a Class 8 truck bearing down on you at 60 mph (97 km/h), you don’t want to have any doubts the engine is going to (restart) just as you are about to pull back out,” he says at a media backgrounder here. “Driver angst about the restart event is one reason OEMs today have said no to start/stop.”

CPT says the current device is geared for 12v electrical systems but is scalable to a 48v architecture, which CPT says auto makers are advancing toward.

Coupled with the higher voltage electrical system, the SpeedStart could provide 10 kW (13 hp) of electrical driving power for up to 30 seconds, reducing engine loads and improving fuel economy, Pascoe says.

That would position SpeedStart as a midrange micro-mild hybrid technology, providing less electrical boost than a higher-voltage, full mild hybrid like Honda’s Integrated Motor Assist powertrain or General Motors eAssist, but costing much less.

“We see this in the lower half of mild-hybridization,” Pascoe says. “This is putting a number of small electrical devices on, (with) the key enabler electronics. We see this as smart use of technology, rather than a big sledgehammer.”

SpeedStart would work with engines up to 4.5L-5.0L in size, CPT says. The power bursts would be mapped precisely to specific engine loads to maximize fuel-economy and carbon-dioxide-reduction gains.

The developer says it will have the 48v version of the device installed on a demonstrator vehicle next year for testing. It expects the higher-capacity electrical architectures to begin to appear on vehicles in 2015-2016 and start to proliferate around 2020.

SpeedStart can work with multiple types of batteries, including advanced lead-acid or lighter-weight, higher-cost nickel-metal-hydride or lithium-ion.

“If you’re in the volume markets (where cost is a factor), you may want to stay with commodity battery technology if you can,” Pascoe says. “There’s some good development going on in lead-acid batteries. They still have a lot to offer, and they have a huge cost advantage.”

CPT already has demonstrated its 12v low-cost LC Super Hybrid micro-mild hybrid technologies, including the SpeedStart system, a Valeo electric supercharger and new lead-carbon batteries, in a Volkswagen Passat with a 1.4L TFSI gasoline engine.

Despite the smaller engine, acceleration equaled that of a 1.8L TFSI engine, while CO2 emissions were cut to roughly 130 g/km from about 150 g/km for the bigger powerplant. Retail cost of the system likely would be in the ballpark of $600-$700.

Going to a 48v version of this micro-mild hybrid approach would trim at least another 10 g/km or so in CO2 emissions, equaling the performance of a Passat equipped with VW’s 2.0L TDI diesel, CPT predicts. Acceleration of 0-62 mph (100 km/h) would be more than a half-second better than the diesel, which already exceeds the 1.8L TFSI engine.

Add-on retail cost, estimated at about $1,000 (including the tab for the 48v architecture), would put the system at least $2,000 below the price of the optional diesel, CPT says.

“The fuel economy is not at (Toyota) Prius levels, but it is heading in that direction,” Pascoe says. “(And) it’s not many thousands of dollars to get this type of fuel economy.”

Hurdles include making sure the belt-driven device performs at temperature extremes and the belt itself can withstand the peak electrical torques possible in a 48v architecture.

It’s unclear where CPT will go with the SpeedStart system. The private-equity-funded developer last year sold its electric supercharger technology to supplier Valeo, which is expected to put the device into production for light vehicles. CPT still owns rights to a commercial-vehicle version of the device.

It could take a similar route with SpeedStart, license another manufacturer for production or supply the unit to auto makers directly.

CPT expects regulators eventually will give stop/start a marketing boost by revising test cycles to take advantage of the technology, nudging fuel-economy ratings upward and giving consumers a reason to shell out the extra upfront cost.

Current fuel-economy test cycles “are becoming a bit of a dinosaur,” Pascoe says. “You’ll see a lot of progress made in the next few years on drive cycles.”