David Gordon Evans

NEEDLE BEARING AXIAL THRUST STUDY

This paper discusses the mechanics of axial forces generated by needle skew in full complement, continuous rotation needle bearings. Experimental measurements of the axial forces and observed needle skew angles are presented for single and double row bearings. Various mechanisms causing the needles to skew are discussed along with design modifications for eliminating or reducing the axial thrust.

Combustion Assisted Belt-Cranking of a V-8 Engine at 12-Volts

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.