Sensors
Thick film oxygen sensor A thick film-type oxygen sensor has been developed by researchers (Keisuke Makino, Hisaharu Nishio, Teppei Okawa, and Katsuhisa Yabuta, NGK Spark Plug Co., Ltd. and Koichi Shimamura, Honda R&D Co., Ltd) that has the unique structure and principle to achieve fast light off and a compact configuration. The main part of the uniqueness is the self-generation of oxygen from exhaust gas, as the reference. It does not require fresh air from the atmosphere as the conventional thimble-type oxygen sensor, and no output is shifted down by the change of the reference oxygen partial pressure. The other advantage is the monolithic nature of the sensing element and heater, which makes the sensor start working in 10 seconds with low power. The combination of these two key technologies enables the oxygen sensor to be small and free from the location issue. As emission regulations tighten, reducing HC emissions during engine cold starts becomes more important. There are strong demands to devise efficient oxygen sensors that control the air/fuel ratio with the least amount of time delay. The conventional automotive oxygen sensor is comprised of a pen cap shaped zirconia element (thimble type) and a ceramic heater (heating the sensing element). The fast light off of the thimble-type oxygen sensor is achieved mainly by increasing the heater power. This fast light off demand has brought more attention to the thick film-type oxygen sensors using zirconia sheet and printing technology. The reason for the efficient fast light off is that the thick film-type sensor has a single body of integrated sensing and heating element that helps maintain a good thermal conductivity from the heater to the sensing element. The heating mass is small therefore the sensor activates quickly. The zirconia oxygen sensor has a thimble-type element with an outer electrode exposed to the exhaust gas while the inner electrode is surrounded by ambient air as a reference. The oxygen sensor generates electromotive force according to the difference of the oxygen concentation between the inside and outside of the thimble. The thick film-type oxygen sensor using zirconia also has an air passage port leading to the inner electrode from the side surface of the element. For sensors using ambient air as a reference it is important to keep the inside oxygen partial pressure stable. Otherwise there is a potential problem of losing the sensor function by exhaust gas intrusion or contamination of the reference gas. Contactless angle measurement Different methods are known using a magnetic field as a carrier of the measurement information between physical value and the sensor. These contactless principles allow a separate encapsulation of all rotating components making such systems robust with respect to pollution and mechanical destruction. Systems based on the magnetoresistive (MR) effect are characterized by the additional feature that they evaluate the direction of the magnetic field, not the field stream. The field strength itself is not important as long as it is above a certain limit. Therefore, MR-based systems tolerate variations in field strength caused by aging or temperature-sensitivity of the magnet as well as mechanical tolerances. A new two-chip solution from Philips Semiconductors (Klaus C. J. Dietmayer) provides an easy and cost-efficient method for building up an application-specific MR angle measurement. MR sensors make use of the fact that the electrical resistance of certain ferromagnetic alloys, such as permalloy, is influenced by external magnetic fields. This solid state MR effect, or anisotropic magnetoresistance (AMR), is easily realized in thin film technology, allowing the production of precise but also cost-effective sensor modules. As the MR effect is naturally an angular effect, its use for contactless angle measurement systems ia a good fit. The underlying principle of operation is simple—the electrical resistance of the permalloy strip changes with the angle between the internal magnetization vector and the vector of electrical current flowing through it. Consequently, to achieve accurate measurements, the only condition to be met is that the internal magnetization vector of the permalloy must directly follow the external magnetic field vector. This is ensured when using external field strength much higher than the internal magnetization. As this strong external field saturates the sensor, the actual field strength has no impact on the measurements. Only the direction of the field is evaluated. This leads to the following advantages of MR angle measurement systems which are independent of the following items:
To support users who want to build contactless angle measurement systems, a new two-chip solution for MR technology is provided. It consists of the MR sensor KMZ41 and the signal conditioning IC UZZ9000. The IC was designed for the sensor and therefore provides an optimized interface to it. It has a standard analog output that operates ratiometrically to supply voltage. Catalyst temperature sensor The development of new systems to reduce exhaust gases is being investigated in response to OBD-II regulations as well as others all over the world relative to the introduction of low exhaust emission gasoline vehicles. Researchers (Atushi Kurano, Sotoo Takahashi, Kaoru Kuzuoka, Denso Corp. and Itsuhei Ogata, Nippon Soken Inc.) have developed a sensor with the following technologies:
The most common structures for thermistor elements are disks, rods, and glass-enclosed structures. In these types of thermistors, an Ag or Pt paste is applied to the thermistor as an electrode after which the thermistor is baked and molded. Such thermistors are heat resistant up to approximately 500°C, but cannot be used in temperatures of around 1000°C. For the new sensor a thermistor-element structure was chosen in which a thermistor and platinum wire electrode were sintered together and thus shrink-fitted. In the manufacture, the thermistor granules were dry molded using a double-holed die, two platinum wires were inserted and sintered at 1600°C. During sintering the thermistor shrunk but was held firmly to ensure close contact with the outside of the platinum wire. The element was made as small as possible to increase responsiveness. However, an element too small would not have the strength required for manufacturing and mounting. A minimum diameter of 0.3 mm for the platinum electrode was chosen to withstand the vibration. To avoid cracks caused by shrinkage of the element when the two 0.3 mm diameter electrodes were sintered together, a 1.6 mm minimum external diameter element was chosen. The 1.5 mm thickness of the element was determined from the minimum length at which strength could be maintained when the platinum electrode was baked. To shorten response time, the design of the temperature sensor was optimized to accommodate the thermistor element. The sensor is made of four parts—the thermistor element, sheath pin, an alumina insulator tube, and a cover. The sheath pin consists of an SUS310S sheath tube and a signal conductor made from two core wires and an MgO powder. The platinum electrode on the thermistor element is joined to the core wires using laser welding. The material used for the cover is also highly heat resistant SUS310S. The cover protects the thermistor from the effect of external exhaust gases. A seal is provided by laser welding between the sheath pin and cover. An alumina tube is built inside the thermistor to insulate it and improve the heat conductivity between the cover and element. To achieve the high response levels required, the thickness of the alumina insulation tube around the thermistor and the thickness of the safety cap had to be minimized, but kept to a level in which strength and heat resistance would be maintained. In the connection between the platinum electrodes in the thermistor element and the core wires in the sheath pin, a constant distance between the element and sheath pin needs to be maintained.
A generic idea of a synergetic system approach and a radar-based near distance sensing device is being investigated by researcher (Martin Kunert, Werner Hoop, Karl-Heinz Eglsedor, and Ludwig Ertl) at Siemens AG. Due to the limited space in the vehicle's front and rear region, a multi-functional sensor system for different applications is envisaged. Since 1991 ultrasonic-based parking aid systems turned up on the automotive market with continuously increasing numbers. Actually systems like ACC based on 77 GHz microwave technology appear on high cost vehicles, which scan an observation zone in front of the vehicle from one to 150 m with an aperature angle of about 10°. For next-generation ACC with stop and go, the observation angle before the vehicle must be enlarged to an amount which demands a broad-looking, near-distance sensing device. Smart restraint systems of future generations with reversible actuators (e.g., pneumatic airbag, motor-driven seat-belt pretensioner) require a so-called precrash sensor which alerts the restraint ECU of an imminent object coming frontal or aside into the car several milliseconds before crash occurrence. The surveillance of the vehicle's blind spots and an indicator of the presence and speed of an object within this area not covered by the rear view mirrors will support the driver during lane-change operation or low speed maneuvering. The fast growing number of elderly drivers will benefit from such driver assistant devices. The key to these systems is the near-distance sensing device. Due to the limited mounting space, cost aspects, and distributed, multi-functional architecture concepts, a proximity sensing device must provide sufficient flexibility to fulfill the different demands for near-field applications. Among the different physical realization principles for near distance measurements radar-based devices offer several advantages compared to acoustic, optical, or thermal methods:
The varying demands of the different systems functions require a flexible sensor concept, which can adapt its performance limits accordingly. To cover the complete vehicle's front or rear surface, a distributed sensor system consisting of at least two radar devices placed at the car body's outer dimensions (e.g. the bumper's right and left corner) is obligatory. The usage of a smart control and processing unit, either implemented with a microcontroller or an ASIC, in the radar front end guarantees the desired flexibility for a multi-functional operation. A common ECU communicates both with each radar front-end module via a local communication protocol and with the vehicle's infrastructure by the appropriate gateway link. The near-distance sensing device system consists of two functional module types and a given number of smart radar modules, and can be easily extended by adding other radar modules. The microwave front-end module consists of a high-frequency circuit, two patch antenna, a microcontroller with some glue electronics, and some signal conditioning stages. The microcontroller provides all necessary control commands, samples the received radar signals, and conducts basic signal processing algorithms. The ECU gathers the processed, condensed information from the front-end modules via a dedicated local bus. The data exchange to relevant subsystems on the vehicle's infrastructure is managed exclusively by the ECU with the respective, subsystem-specific protocol. This communication link is also used to provide the near-field sensing ECU with vehicle-specific information (e.g. steering angle, reverse gear, or driving speed). The bidirectional high-speed Can-bus between front-end modules and ECU manages both control and information exchange and avoids data package collisions on the communication link by ECU bus mastering. Special command sequences of the ECU cause the radar modules to conduct a special function task and send back the information in a specific order and time frame. Alternatively, event-triggered data transmission of the radar front-end devices, previously set in a scanning operation mode by the ECU module, can be established for time-critical applications like precrash sensing. From the many possible radar operation principles, a combination of pulse, Doppler, and FMCW radar is selected to best match the varying performance requirements of the envisaged functions. Among the possible operating frequency bands, stipulated by national and international regulations, the ISM frequency band from 24.00 GHz to 24.25 GHz was selected for the near-field sensor.
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