Navistar International Transportation Corporation

Essex Group, Inc.

Michael B Durant

Lawrence H Kuhn

Glen C Young

The spring-operated parking brakes of a tractor-trailer are controlled by a novel electro-pneumatic system. Pneumatic valving through which compressed air is conducted is mounted on the tractor chassis and coupled via an electronic circuit to two hand-operated control devices on the dash of the tractor cab, one for the trailer parking brakes only and the other for the tractor parking brakes. The latter device inherently operates the trailer parking brakes via the circuit if they are not already applied, and the circuit incorporates a sequencing function for operating the trailer brakes slightly before the tractor brakes when the tractor parking brake control is operated. Compressed air for the system is obtained via an engine-driven compressor which charges a tank. A pressure transducer monitors tank pressure for the circuit with the circuit maintaining tank pressure through selective loading and unloading of the compressor. Purging of the dryer is coordinated with compressor unloading. The pressure transducer also interacts with the parking brake control devices and the parking brakes such that when the pressure drops below a certain level, the parking brakes are automatically applied. The circuit also gives an alarm before the pressure reaches that level.

Electro-pneumatic tractor-trailer brake system

In an electronic control system, as for instance, one employing a microcomputer, a timing reference signal supplied to the microcomputer, typically from the AC supply line, is monitored for continuity and integrity by determining whether that signal occurs or recurs some predetermined number of times relative to a measuring interval. The measuring interval is established by an event provided by the microcomputer and which recurs with a generally known time relationship to the timing reference signal. Failure of the timing reference signal to occur or recur within the measuring interval is interpreted as a failure of the timing reference, and a reset command is automatically executed to automatically reset or initialize the control system. A display, for instance associated with an appliance such as a microwave oven, may be repetitively scanned at some normal interval in response to the programmed control of a microcomputer. The measuring interval for monitoring the timing reference may be established from the display scan signal and the monitoring operation may be performed with a program stored in the microcomputer.

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Fort Wayne, IN, United States of America

Michael B Durant