Seamless Solution for Electronic Power Steering 2006-01-0593

The number of safety critical automotive applications employing high current brushless motors continues to increase (Steering, Braking, and Transmission etc.). There are many benefits when moving from traditional solutions to electrically actuated solutions. Some of these benefits can include increased fuel economy, simplified vehicle installation and packaging, increased feature set, improved safety and/or convenience, simplified unit assembly and modular testability prior as well as during vehicle manufacturing.

The trend to implement brushless motors in these applications (which require electronically controlled commutation) has also brought with it the need for powerful inverters, which primarily consist of Power MOSFETs and MOSFET Driver ICs.

This paper reviews the challenges associated with the design of safety critical electronic systems which combine sensing, control and actuation. A key requirement for applications demanding 100A and above is the implementation of a powerful inverter, an example of which will also be discussed. Reliable operation under low voltage conditions in harsh automotive environments are reviewed and additional requirements resulting from safety relevant applications will be outlined using Electronic Power Steering (EPS) as an example. By means of this example it will be shown how the components of the inverter (MOSFETs and Driver IC) help to enable hardware design engineers to implement inverters which meet the requirements in safety relevant applications by keeping in mind cost targets, space constraints, thermal boundary conditions and the like. The components’ features and functions will be covered along with their impact on the Safety Integrity Level (SIL) viewed from the System level.

Finally, an overall look will be taken inside an EPS ECU focusing on the other semiconductors required as well as the options available to partition them.