Lower fuel consumption and reduced CO2 / NOX emissions with unchanged engine power are the main drivers for the increased use of variable geometry turbochargers and EGR valves in the cars.
In the last 10 years, many applications have been significantly improved in the power train thanks to fully automated control systems. Thereby, high-precision sensors provide the position of various actuators in the engine area.
In the past, a majority of these sensors have been based on one-dimensional, linear Hall-effect sensors. Meanwhile, the trend is to utilize direct angle sensors which allow a temperature stable multidimensional angle measurement with elementary magnetic circuits.
EGR works by recirculating a portion of the engine’s exhaust gas back into the engine cylinders leading to reduced fuel consumption of the vehicle and less CO2 emissions. The engine control unit needs an actual position of the EGR valve to get an accurate and efficient control. The EGR Valve working principal is based on a linear displacement of a valve rod (see Fig. 1). The typical range of measurement is of 10mm.
Such distance with an ambient temperature up to 160°C (320 °F)can be precisely measured by a 2D Hall: either directly via linear displacement measurement of a small bar magnet or via rotational movement by means of a single disc magnet.
The two capacitors assembled in the sensor package have a value of 100 nF and can reliably work in ambient temperatures up to 160 °C (320 °F). This is particularly important in applications such as EGR, turbo actuators or bypass valves, because exhaust gas systems are exposed to higher temperatures. The capacitors meet the demanding EMC requirements in the 50 V-version. Compared to competitors solutions, the HAC 37xy can withstand the hard General Motors GMW3097 85-V-pulse (DCC) without any further passive components.
The HAC 37xy has been classified as Class A (A = max. ± 50 mV output deviation) for immunity BCI tests up to 300 mA according to ISO 11452-4 (open-loop) and PSA B21-100-C (closed-loop).
Thanks to his "virtual offset feature", the HAC 37xy is the perfect solution for linear measurement required in applications as EGR and Turbo charger. It allows increasing the accuracy or reducing the system cost by using smaller magnets: for example a magnet with 5 mm length~ can achieve <1% linearity error over the full temperature range of -40 °C to 160 °C (-40 °F to 320 °F).
By using the Hall sensor with SENT interface, the HAC 37xy is able to transmit the chip-temperature and the position information via the "fast channel" or over several frames via the "Slow-Channel". The temperature information is very important in the exhaust area and it saves the use of a separate temperature sensor.