A low cost and mass efficient Engine Stop-Start (ESS) system was developed using a production 1.9 liter four-cylinder spark-ignition engine mated to a four-speed automatic transmission. The ESS powertrain uses a 42-volt belt-driven electric motor-generator mounted to the side of the engine to enable fuel off-on transitions during decelerations and stops. A control scheme was developed which balances fuel economy and emissions while minimally affecting driveability. Tests have shown EPA City fuel economy gains of about 12～14 percent while maintaining the same emissions classification as the baseline production vehicle. The EPA Highway fuel economy was increased by about 1 percent, resulting in an EPA Composite fuel economy gain of about 7 percent.
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