Abstract: In this paper, a new dosing unit is presented for diesel exhaust fluid (DEF) dosing in combustion engine exhaust emission selective catalyst reduction (SCR) systems. The dosing unit is a plunger-sleeve pump nozzle system driven by a charged solenoid, and is pump-end controlled by pulse width modulation (PWM) signals. The core characteristics of the unit include both metering precision control and failure diagnosis methods. In this study, both physical-mathematical analysis and experiments were carried out. A so-called whole state T3 metering theory was developed by studying the system using a physical-mathematical model based on energy conservation. The study showed that the liquid discharge, which is associated with the plunger-sleeve relative position, correlates well with a measurable variable T3. Experimental investigations verified that the metering results were independent of the state variations in some range and that metering is controlled with high precision. Two typical DEF dosing systems based on the dosing unit and some specific failure modes are introduced. Significant variation of the parameter T₃ in the T3 model is useful for the detection of specific failure modes.

Key words: Diesel exhaust fluid (DEF) dosing unit; Plunger-sleeve pump; T3 metering theory; Sensor-free diagnosis

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