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In order to expand the applicable range of in-vehicle LANs down to popular cars, drastic cost reduction is essential. In addition, an in-vehicle LAN with high transmission rate and advanced functioning is extremely important for the further spreading of vehicle electronics intended to enhance vehicle intelligence. We developed the Protocol for Automotive Low and Medium Speed Network (PALMNET) as an in-vehicle LAN system and put it into practical use in 1990. Based on this, we developed a new communication protocol and three ICs for an in-vehicle LAN called the Advanced Protocol for Automotive Local Area Multiplexing Network (Advanced PALMNET), which satisfies the above-mentioned requirements and covers the medium-to-low transmission rate (up to 125kbps) to high rate (up to 1Mbps).

The latency time of class C in-vehicle LAN systems was evaluated in order to analyze the difference in latency time between the non-destructive CSMA/CD (CSMA/CD+NDA) and the token passing selected as the high speed LAN protocols. The evaluating method was constructed by combining simulation and an analysis equation. As a result, the limits of traffic volume available for vehicle application were approximately 80 to 90 % for the CSMA/CD+NDA and 30 to 40 % for the token passing at a transmission rate of 1 Mbps.

At present, various communication protocols for an automotive distributed control multiplex system that aims at solving wire complexity and meeting the requirements of high reliability and open system flexibility have been proposed and installed in production cars. The requirements for an automotive distributed multiplex system, especially reliability, flexibility, and economy have been analyzed in detail, and as a result a new communication protocol based on SAE J-1850 has been developed. This paper describes the design philosophy and technical features of the protocol, named PALNET (Protocol for Automotive Local area Network) and the result of evaluation with the experimental system. PALNET covers moderate speed signals in vehicle electrical and electronic system. Main technical features of PALNET are as follows. Introduction of a new acknowledgement method named ANC (Acknowledgement for Network Control) secures high reliability of data communication.

A new electronic controller for continuously varying the speed of windshield wiper motor has been developed. It permits conventional wiper motors without any modification to be set at any speed, low to high, for sophisticated wiper operation. Speed control is based on PWM and power MOS FETs. Fundamental problems peculiar to this method such as audible noise generation, R.F. noise generation, starting torque reduction, and speed drift due to load variation have been solved. Further, provided with the controller, the motor can keep its preset speed constant against changes in voltage, temperature, and torque. The controller, packaged in a small unit, is available at a low cost, and durable under severe automotive environment.