Engine Monitoring System (EMOS) plays a crucial role towards engine safety and monitoring for low cost commercial vehicles not equipped with a full-fledged Engine Management System (EMS). The EMOS system mainly focuses on monitoring of coolant temperature, alternator belt failure, and lubrication oil pressure and coolant level indication
This paper describes various engineering design considerations for balancing the application requirements with implementation costs. It also highlights some common pit-falls in detecting alternator failures leading to nuisance trips as well as system design considerations involved in matching the gauge indication accuracy with the coolant high temperature trip point.
The system designer needs to take into account, difference between alternator belt slippage versus total belt failure condition and implement different control strategies accordingly. The coolant temperature trip-point feature needs to fix the optimal accuracy requirements based on the end-application and cost constraints. The precision/tolerance of the coolant temperature sensor (usually NTC sensor) and the temperature gauge indication needs to be compatible with each other otherwise the resulting discrepancy between the indicated temperature and actual temperature might result in engine trip by EMOS is likely to annoy the driver.
Hardware/software implementation aspects which realize the application solution based on the above considerations are explained. The power-supply needs to cater to a wide battery voltage range from 8 to 32 volts taking care of all automotive transients. The choice of component tolerance for reading various sensors should also balance cost and application accuracy requirements. The sensor supply can also be derived directly from the battery rather using a precise regulated supply which adds to the cost. A clever software strategy can read the instantaneous battery voltage along with the sensor raw data and correlate the same for deriving actual sensor input within required application accuracy. Alternator belt failure indication strategy needs to consider false alarm condition occurring due to open-circuit of the warning indicator bulb filament rather than actual belt failure condition. Whereas belt-slippage condition, if demanded by the application, needs to compare engine speed/vehicle speed signal with the alternator “W” terminal signal frequency.
Finally the paper sums up by correlating some field experiences with the actual implementation and summarizes the lessons learnt during the same.