The Dawn of the Vehicle Microprocessor

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In the spring of 1973, a project was initiated to develop a vehicle computer using a microprocessor. The effort was executed at the Electronic Control Systems Department within the GM Engineering Staff. This ECS Department was created in 1971 by Trevor O. Jones under the directive of Edward Cole to advance the utilization of electronics in automobiles. Prior to this effort, the control functions implemented by this computer had been performed with analog circuitry or mechanically.

The project encompassed algorithm development using digital logic circuitry, custom designed interface circuitry, microprocessor and memory circuitry, and software implementation of the algorithms. Individual teams of engineers were formed to implement each aspect of the project and then worked together to create the microprocessor controlled vehicle. By mid-summer 1974, two Buick vehicles (designated Alpha IV vehicles) containing microprocessor controllers were functional and were being tested and evaluated.

Three vehicle speed control functions included cruise control, four wheel anti-lock brake control, and traction (or anti-slip) control. These functions utilized high resolution wheel speed counter interfaces to the 4 bit microprocessor and efficient algorithms to perform all control functions within a 15 millisecond refresh cycle. Besides these vehicle speed control functions, the computer performed speed warning, speed limiting, and automatic door lock functions and displayed the vehicle speed in digital and analog formats. The odometer and trip odometer features were maintained in non-volatile memories and displayed in digital formats. Other display features included time of day and elapsed trip time.

Engine control features on this vehicle included ignition spark advance and dwell controls. To accomplish these features accurately, high resolution counters were utilized as inputs to and outputs from the microprocessor. The microprocessor algorithm was refreshed every 15 milliseconds and had to respond sudden engine accelerations and decelerations. The engine speed was displayed in a digital tachometer format.

This system concept was presented at the Second Convergence Convention and published as SAE Document 750432 - Application of Microprocessors to the Automobile Authors: T.O. Jones, T.R. Schlax, & R.L. Colling; Published February 1975

Following this project, another vehicle (designated Alpha V) was developed with a microprocessor controlled display system. It demonstrated many of the same functions in the previous vehicles. Simultaneously, two custom integrated circuits were specified and designed. One device was an interface circuit for the microprocessor to communicate with vehicle sensors. The other device was intended to calculate and display fuel economy; instantaneous and average miles per gallon.

These demonstration vehicles provided an impetus for Delco Electronics to begin a development effort on a custom automotive microprocessor design. The algorithms and interface circuitry used in these projects provided a good knowledge base for this microprocessor specification. By the early 80’s, microprocessors were integrated into production vehicle systems.


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