Combustion Assisted Belt-Cranking of a V-8 Engine at 12-Volts 2004-01-0569
Implementation of engine turnoff at idle is desirable to gain improvements in vehicle fuel economy. There are a number of alternatives for implementation of the restarting function, including the existing cranking motor, a 12V or 36V belt-starter, a crankshaft integrated-starter-generator (ISG), and other, more complex hybrid powertrain architectures. Of these options, the 12V belt-alternator-starter (BAS) offers strong potential for fast, quiet starting at a lower system cost and complexity than higher-power 36V alternatives. Two challenges are 1) the need to accelerate a large engine to idle speed quickly, and 2) dynamic torque control during the start for smoothness. In the absence of a higher power electrical machine to accomplish these tasks, combustion-assisted starting has been studied as a potential method of aiding a 12V accessory drive belt-alternator-starter in the starting process on larger engines.
The combustion-assisted cranking system has been implemented on a 5.3L V-8 engine with automatic transmission in a full-size truck. Integration of the BAS system controls with powertrain fuel and spark management shows the importance of combustion-assist within the first several compression events. The use of a cylinder-event-based (CEB) spark strategy was found to benefit the feel of auto-starts, as measured by passenger seat track vibrations. Introducing fuel into the cylinders during the shutdown showed up to 40% improvement in engine start times. Furthermore, this paper reports the feasibility of auto-starts from shutdown fuel in terms of start consistency and shows the need for a quick synchronization process of the powertrain control module if a 12-volt system is to be successfully used.