On Electronics: Oct. 2013
Stop-Start. Millions of Times
Three years and more than 2.4-million stops and starts later, the engine restarted each time.
Controlled Power Technologies (cpowert.com) hooked up a SpeedStart stop-start system to an engine in October, 2010. They ran it 24-hours-per day until September, 2011, when it reached 1.2-million restarts. That’s a restart on average of every 12 seconds, 300 restarts per hour, 7,200 restarts per day for 350 days. OEMs, says CPT, require systems to be capable of 150,000 to 300,000 restarts. They initiated a test on a second unit SpeedStart in June, 2011. At last report, it was still running. It passed its 1.2-million start/stop sequence in February, 2013. This test will continue until it fails to help determine the likely maximum service life. CPT’s goal is to make systems that do not fail over a 15-year, 250,000-mile vehicle lifespan.
The rigorous testing helps prove the reliability of stop-start systems, which are useful in the quest to meet more stringent fuel economy standards, CPT says. In addition to SpeedStart, the company also produces products including an electronically charged supercharger and an exhaust energy recovery system.
“Fuel economy targets require reduced stop-inhibits, not just stopping the engine when the driver places the transmission in neutral,” said Peter Scanes, CPT’s hybrid product group manager. “Latest implementations allow frequent stop-start events in crawling traffic and future coast-down strategies. Switching off the engine, but preparing for immediate restarts if the driver demands acceleration, will further increase the frequency of stop-starts.
“We needed therefore to demonstrate as convincingly as possible the near-zero probability of failure during the lifespan of a vehicle as well as the ability to achieve the maximum number of re-starts, because one of the most cost effective solutions for low fuel consumption is simply stopping the engine at every single opportunity—even if it’s only for a few seconds every second counts,” Scanes explained.
SpeedStart is said to be the first liquid-cooled, switched-reluctance motor-generator developed for automotive stop-start. The system is designed for 12-V, 24-V and 48-V applications. CPT said its durability stems in part from sealing off the integrated control and power electronics so dirt and other debris do not enter the device, as well as thermal management provided by plumbing the liquid-cooled unit into the engine’s coolant system.
At 12 V, the company said SpeedStart can generate up to 3 kW of power at 90% efficiency and that the stop-start technology provides a CO₂ reduction and fuel savings of up to 20%.
The technology is production ready and is expected to appear on a new generation of micro hybrids appearing in showrooms by 2015.