Sensor technology to reduce diesel engine emissions
Reducing carbon dioxide emissions is the hottest topic in the automotive industry today. The European Commission recently announced a roadmap for obtaining safer and more environmentally friendly vehicles by 2012. Significant changes in the way consumers buy cars also confirm that consumers want the most fuel-efficient cars that can meet their personal and professional needs. Through advances such as hybrid fuel technology, automakers are introducing new cars that reduce carbon dioxide emissions. There are also technologies dedicated to this goal, such as Blue MoTIon, EconeTIc, and Efficient Dynamics.
It is also a fact that the pollution rate of diesel engines is higher than that of gasoline-powered cars. In particular, diesel particles are harmful to the human body, causing lung discomfort, cancer, and heart disease. Older diesel engines emit larger visible particles, like black smoke, while the particles emitted by newer engines are generally too small to be seen with the naked eye.
To make these emissions cleaner, car manufacturers have built diesel particulate filters (DPF). Since 1980, these filters have been used in off-road vehicles, and since 1996 in some ordinary cars. DPF can now capture diesel soot particles as low as 2.5 microns, thus reducing particulate emissions from 60% to 7%. DPF uses porous ceramic materials, which will eventually saturate and require cleaning and regeneration. For such maintenance, the DPF needs to be heated to an exhaust temperature above + 600 ° C. In order to achieve this higher-than-normal temperature, the ECU (Electronic Control Unit) will temporarily delay the fuel injection and limit the suction. At this time, the sensor becomes a key control element: by measuring the pressure drop on the filter with a pressure sensor, the most effective time to start the regeneration process can be determined.
Interface implementation
Taking the diesel filter module as an example, we installed a differential pressure sensor using traditional varistor elements in the DPF. This sensor checks a small pressure range, generally 0 to 15 psi. A sensor interface IC (such as the MLC90320 CMOS analog sensor interface from Melexis) is connected to the output of the sensor to form a resistive Wheatstone bridge circuit. This interface can convert a small change in resistance (usually a few millivolts) into a considerable change in output voltage. With this structure, the circuit can compare the pressure signals before and after the filter (Figure 1). The interface chip amplifies and corrects the sensor signal and converts it to a value that the ECU can recognize. When the DPF is saturated, the interface will detect a large pressure difference between the signals before and after the filter. The interface IC amplifies and compensates this difference and transmits it to the ECU. This process enables the sensor interface to control the communication between the detection element and the ECU, ensuring the continuous normal operation of the filter.
Sensor interface
In the above example, the varistor detection element is connected to the input terminal of the sensor interface, which compensates the signal for gain and offset to determine that there is a well-calibrated output signal. In addition, 3-bit and 10-bit digital-to-analog converters (DACs) are used in different coarse adjustment stages. The output architecture of this special interface uses another 10-bit DAC to accurately calibrate the output variation range (Figure 2). ).
The device's architecture can easily detect a few millivolts of sensor output and obtain a precise output range of 4V. In order to ensure the smooth compensation adjustment of the interface chip, we added a rough compensation correction to compensate for the large offset change of the detection element, and used adjustable 10-bit compensation. When considering temperature issues, the sensor interface can also be connected to internal or external temperature sensors.
However, if the ambient temperature of the sensor is different from the ambient temperature of the interface, it is best to use only one external temperature sensor. Connect an external resistor to the temperature chain used to adjust the offset and gain, and the interface can perform accurate 10-bit temperature measurement when necessary (Figure 3). In this way, the external temperature sensor can be installed as close as possible to the pressure sensor.
Programmable clamp
Another unique property of the sensor interface is its ability to implement programmable clamping at low and high output levels. Clamping ensures the sensor's ability to detect the lowest and highest output levels, and the ECU can check whether the sensor's output is within an acceptable range. In addition, the sensor interface in our example also integrates fault detection and is therefore suitable for a range of automotive applications. When it detects internal and external faults, the device can detect the bad connection of the detection element.
If the chip receives an incorrect input level from the sensor, such as lower than 1.5V or higher than 3.5V, there may be a short circuit to ground or power supply, and the IC will produce an output level that exceeds the clamping level range. The ECU thus detected the event. This dedicated interface IC can program the sensor interface through the actual connector. The module containing the detection element and interface is housed in a housing, and only the application pins are connected to the outside of the module. There is no need to add other communication lines, because the output pins can be used as analog output pins as well as communication pins. Through the short circuit detection, the IC knows that the user is requesting the pin for communication. To ensure that memory parameters do not change during a short circuit, this test is based on a specific sequence of actions. In addition, the interface chip includes an option to lock the EEPROM to avoid accidentally changing the calibrated device. In fact, by using the output of the interface, we can communicate with the chip and correct the parameters in the EEPROM with user-defined characteristics.
There are existing evaluation boards for calibrating the interface. These boards include all the hardware, accompanying software, and production software needed to communicate with the interface. The production software can control all necessary production equipment and communicate with the equipment to quickly calibrate hundreds of samples.
Conclusion
Sensor interfaces are everywhere in the car. They convert the sensor signal into a readable format, and at the same time filter out disturbing external components to ensure that accurate information is sent. We can find various types of sensors in commonrail systems, suspension and transmission systems, and HVAC applications, fuel injection systems, engine control, brake antilock brake systems, and many other places in automobiles. They are so widely used that people can almost forget them. Understanding their performance can facilitate the use of these irreplaceable products in more and more applications.
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Changzhou Changyuan Electronic Co., Ltd. , https://www.changyuanelectronic.com