Development of a Smart Analog Integrated Circuit for Electronic Control of an Automotive Variable Power-Steering System

A smart analog integrated circuit (IC) is developed for use in an electronic control unit for an automotive variable power-steering system. This IC accepts a vehicle speed signal as its input, performs signal processings such as frequency to voltage conversion and function generation, and then as its output generates a pulse width modulated (PWM) signal whose duty corresponds precisely to a given piecewise linear function of the vehicle speed. The PWM output is used as a driving signal to a power MOSFET for the actuation and control of a linearly variable solenoid valve to vary the force needed for steering effort in a prescribed relation to the vehicle speed. The IC is fabricated by monolithic bipolar integrated circuit technology and has about 750 device elements in a chip size of 5.7 by 3.1 mm². It is enveloped in a shrinked dual in-line package with 24 pins. It incorporates on one chip all the signal processing, diagnostic, and compensating functions necessary for electronic control of an automotive variable power-steering system. This paper gives a detailed description of the unique functions and features of the IC together with the improved performance of the system.