Automotive Exhaust Fumes Emissions Are Sensed and Controlled By Reed Sensors REED RELAYS REED SENSORS REED SWITCHES Introduction Trying to find a sensor that will function on the underbelly of an automobile where ice, snow, oil, dirt, grime, very high temperatures and very low temperatures may exist at any given time represents a very difficult objective. The muffler system alone may have temperatures on part of its system in the several hundred degrees C range. Catalytic converters on the muffler system have a valve that must have its position sensed in order to automatically adjust the fuel mixture minimizing exhaust fumes. Auto designers have turned to MEDER’s Reed Sensors. Figure 1. MK14 Sensor physical layout Features • The reed sensors reliably operate between 50˚C to 150˚C • Magnet and Reed Sensor are isolated and have no physical contact by typically having the magnet mounted on the valve in the catalytic converter and the Reed Sensor mounted and positioned to accurately pick up the motion of the valve Figure 2. Normal amounts of exhaust fumes move through the catalytic converter slightly moving a valve but not enough to activate the reed sensor. • The reed switch used in the Reed Sensor is hermetically sealed and is therefore not sensitive to rough, wet, oily dirty environments that clearly exist on the body of the car exposed to the pavement • High temperature plastic and Teflon leads used • The magnet is not affected by its environment • Tens of millions of reliable operations • Cylindrical mounting and screw fastening mounting using high temperature lead wires • Contacts dynamically tested Applications • Ideal for sensing the motion of a catalytic converter valve in the dirtiest, most temperature diverse environment on the bottom side of an auto Figure 3. Excessive amounts of emissions will move the valve inside the catalytic converter into proximity with the reed switch sensor activating the electronics. Reed Sensors Control And Minimize The Exhaust Emissions In Catalytic Converters The world is now fully aware that we humans are affecting our planet in a negative way by adding vast volumes of pollution to the air we breathe. This has affected the ozone and CO2 levels in our atmosphere. The biggest polluter has been singled out as coming from the exhaust fumes of our automobiles. Catalytic converters have been mandated worldwide on all automobiles to control the gas emissions in the auto exhaust. Following these gas emission back up into the engine, we find them occurring when air is mixed with the fuel and ignited by a spark. This produces a mini explosion that drives the pistons, directly affecting the drive train, in turn moving the car forward. This explosion can be efficient or inefficient. If it is inefficient, it will use more fuel and increase exhaust emissions. MEDER electronic Application MEDER electronic AG | Germany | tel.: +49(0)7731/8399-0 | Email: [email protected] MEDER electronic Inc. | USA | tel.: +1 508.295.0771 | Email: [email protected] Page 1 of 3 www.meder.com Automotive Exhaust Fumes Emissions Are Sensed and Controlled By Reed Sensors REED RELAYS REED SENSORS REED SWITCHES Specifications Operate specs Min Max Units Must close distance 5 25 mm Must open distance 5 25 mm Hysteresis Load Characteristics Switching voltage Switching current Carry current Contact rating Static Static Contact resistance Dynamic contact resistance Breakdown voltage Operate time Release time Operate Temp Storage Temp Typical 50% Min Max Units 200 0.5 1.5 10 150 200 320 0.5 0.1 -50 150 -55 150 V Amps Amps Watts mΩ mΩ V msec msec °C ° The exact balance of this explosion has many variables: octane level, air temperature, engine temperature, moisture in the air, etc. Since this is something that cannot be set at the factory, an adaptable approach that takes into consideration all the variables must be used. So to further reduce these gas emissions, auto designers found that sensing the movement of a valve mounted in the catalytic converter that moves relative to the volume of emissions can feed back information to make adjustments. This moveable valve approach in the catalytic converter was chosen because in can take all the variables into consideration. However, now the problem became how to detect this movement in such a way to feed back that information to the onboard computer so that adjustments could be made to the air/fuel mixture. MEDER’s reed sensors were chosen. Because of the adverse environment the reed sensor needs to operate in, the hermetically sealed reed switch within the reed sensor is essential. Furthermore, only very high temperature plastic packaging along with teflon lead wire can be used. Also, the magnet used on the moveable valve must be a high temperature Alnico type capable of dealing with temperatures as high as 400˚C. Essentially as the valve shifts its movement the reed sensor will activate sending a signal back to the on-board computer. It will in turn make adjustments to the air/fuel mixture, thereby maximizing the burn efficiency, producing minimal exhaust emission. The reed sensor is a excellent choice because it can operate reliably from -50˚C to 150˚C and represents an economical way to carry out the sensing function. Because MEDER’s sensors use hermetically sealed reed switches that are further packaged in strong high strength plastic, they can be subject to rough treatment and environmental concerns such as dirt, grease, and moisture found on the bottom side of a car. Consider some of the below options in cylindrical and rectangular versions for end limit sensor or other similar applications. Cylindrical Panel Mount Series Series MK03 MK03 Dimensions mm Dia 5.25 L 25.5 Illustration inches inches 0.207 1.004 MK14 MK14 Dia L 4 25.5 0.157 1.004 MK18 MK18 Dia L 5 17 0.197 0.669 MK20/1 MK20/1 Dia L 2.72 10 0.107 0.394 MEDER electronic Application MEDER electronic AG | Germany | tel.: +49(0)7731/8399-0 | Email: [email protected] MEDER electronic Inc. | USA | tel.: +1 508.295.0771 | Email: [email protected] Page 2 of 3 www.meder.com Automotive Exhaust Fumes Emissions Are Sensed and Controlled By Reed Sensors REED RELAYS REED SENSORS REED SWITCHES Rectangular Screw Flange Mount Series Series MK04 MK05 MK05 MK12 MK12 Dimensions mm W 13.9 H 5.9 L 23.0 W 19.6 H 6.1 L 23.2 W H L 14.9 6.9 32.0 Illustration inches inches 0.547 0.232 0.906 0.772 0.240 0.913 0.587 0.272 1.260 **Consult the factory for more options not listed above. ** MEDER electronic Application MEDER electronic AG | Germany | tel.: +49(0)7731/8399-0 | Email: [email protected] MEDER electronic Inc. | USA | tel.: +1 508.295.0771 | Email: [email protected] Page 3 of 3 www.meder.com