Electronically Controlled Transfer Case: Sensing, Control and Actuation

The increasing demand of four-wheel drive vehicles is pushing the market for more optimized transfer cases. In modern cars the transfer case is usually controlled electronically because this provides more design freedom and the possibility of diagnostics feedback and direct control by the powertrain ECU. A typical transfer case control would include different sensors for angle-rotational speed and position sensing, a keypad for the mode selection by the driver, a microcontroller to compute the information and some high current drive circuitry for driving the actuators. But, while SUV's are known to provide ample space for the passengers, the electronics cannot claim that luxury. With every function added the available board space per function is getting smaller and the additional power dissipation is of concern. This is especially true for high current components like the transfer case motor driver.

This paper describes a system solution for an electronic transfer case control and the implications that arise for the components involved for sensing and actuation. It is shown how the requirements for board space and power dissipation can be met by using an intelligent circuit concept and state of the art chip-on-chip and chip-by-chip technologies.