It has usually been the rule that monitoring another parameter meant adding another sensor. The advent of virtual sensing has changed that.
Clever engineers are increasingly using input from a couple sensors to monitor a third parameter. That saves component costs and complexity, adding only the code needed to determine the additional parameter.
This technique is already seeing use in production. For example, the first E85 vehicles had an ethanol sensor, but General Motors has largely eliminated that part.
“The majority of E85 vehicles have virtual ethanol sensors,” said Ken Kridner, Engine Management System Manager at GM. “We look at the air/fuel mix and detect it based on the oxygen sensor.”
Many virtual-sensing applications are in critical aspects of vehicle operation. Ethanol sensing impacts both fuel consumption and emissions. Other sensors are being used to virtually monitor other aspects of emissions control.
Increasingly, exhaust stream components such as NOx (oxides of nitrogen) and CO (carbon monoxide) may be predicted using sensors in other parts of the system. Virtual sensing is also being used to yield more information on oil properties.
“By referencing a lookup table resident in the EEPROM of a pressure transducer, we may be able to determine oil temperature relative to a specific lubricant when we know the media's pressure,” said Steve Smith, Transportation Sales Director at Custom Sensors & Technologies. Sometimes, it may also be necessary to cross-reference engine speed (rpm) and barometric pressure, which determines the altitude of the vehicle, he added.