Continental has begun production on a new urea sensor that it says will help make diesel exhaust gas aftertreatment more efficiency and reliable.
The company says that sensor-aided denitrification supports fulfilment of legal requirements and will help build driver trust in vehicle emissions.
The urea treatment process depends on precise monitoring, and Continental is launching such a sensor for the first time to measure the quality, level and temperature of the urea solution in the tank.
“Our urea sensor technology supports SCR systems. First of all, the sensor provides the data basis to adapt the injected amount of urea to the instantaneous engine load. Secondly, this data is required for the onboard diagnosis of the exhaust-gas aftertreatment function. In addition, the sensor monitors the urea fill level in the tank to help the driver top-up AdBlue in good time”, said Klaus Hau, head of the sensors and actuators business unit in Continental’s Powertrain Division.
The new sensor contains piezo elements, a negative temperature coefficient (NTC) resistance thermometer, and an application-specific integrated circuit (ASIC), all of which Continental is already using successfully for measuring oil levels. Ultrasonic signals measure both the urea concentration in the water and the tank’s fill level. For this purpose, the urea sensor can either be welded into the tank or into the pump unit.
“Whenever precision is a must in the vehicle, sensors are in great demand,” adds Hau. “SCR provides a prime example. If an SCR system is to reach its maximum efficiency, the injected amount of AdBlue will have to be dosed precisely in accordance with the exhaust-gas flow and composition”.
Continental says that several factors are at work here. The injected amount of urea solution needs to be calculated for the instantaneous engine load. In order to calculate the right amount to be injected, the actual urea content in the AdBlue solution (its quality) needs to be known. Also, the urea solution must not get too cold. Therefore the temperature within the urea tank has to be monitored in order to ensure constant system availability by activating a heating system when needed.
There must also be sufficient urea in the tank the ultrasonic sensor principle offers the ability to measure the liquid from outside the tank. This is not only a key element for freezing resistance, it also avoids any corrosion from occurring at the sensor element or the electronics.
The innovative urea sensor can provide all this data as an input value for the urea metering, according to Dr Wighard Jäger, head of R&D fluid sensors, business unit sensors and actuators: “An increased SCR control quality helps to avoid overshooting or undershooting during the urea metering process. Once you dynamically control the injected urea amount by processing the sensor signal, it is much less likely that either NOx or ammonia will slip through the SCR catalyst.”
Research and development work for the urea sensor was conducted at Continental’s facility in Nuremberg, Germany, and production is taking place at Frenstat in the Czech Republic.
February 9, 2016