Focus on automotive sensor applications

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Focus on the application of automotive sensors

for many years, sensors used to measure pressure, temperature and acceleration have been the protagonists of automotive electronics. However, a large number of systems with such functions, such as fuel injection control, fuel economy and safety systems (including "smart" airbag and tire pressure monitoring), have gone beyond the level of placing a sensor where necessary and sending the sensing signal back to the control unit

the emergence of various digital bus systems can easily realize centralized processing and simplified harness connection, and make it possible to make full use of the advantages of processing intelligence integrated in the sensor responsible for data acquisition. However, such an architecture also brings hidden worries about reliability; In addition, typical automotive applications also face many challenges in continuously reducing costs

high speed buses such as controller area network (can) and more powerful FlexRay bus are traditionally used in occasions requiring intensive calculation and rapid processing such as engine and chassis control. The low-cost, single line connected local interconnect (Lin) is developed for body electronic applications that do not have strict speed requirements, such as seat positioning and temperature control, but focus on simplicity and low cost. Single wire Lin also means lighter weight, resulting in better fuel economy

matthiaspoppel, global advanced embedded control marketing manager of Texas Instruments (TI), said that the ability to place the control IC and sensor on the monitored mechanical part can save space and simplify the processing of the system CPU. But he went on to say that the reliability of this mechatronic sensor, which integrates machinery and electronics, is a problem. "It is not flexible enough (for design engineers), because there may only be one supplier for such integrated sensors, and there are usually several suppliers for components composed of discrete devices," he added

according to poppel, "the transformation to 32-bit MCU and the satellite processor/sensor structure connected to the mechanical part have yet to be tested." For example, PCB equipped with mechatronicsensor attached to a measuring device must be tested and verified to ensure stability and reliability under any expected action, load, temperature and vibration conditions

stevehenry, senior marketing manager of programmable controller power in Freescale Semiconductor sensor business department, also mentioned the concern about sensor reliability and the impact of packaging on it. "For example, the challenge for the sensor accelerometer is that the user wants to have a smaller package for the integrated sensor and controller IC."

henry indicated that Freescale provided a 6mm × 6mmqfn surface mount MEMS devices, but the bare chips must be stacked to meet the smaller overall packaging requirements, so that they can be mounted in an increasingly compact space

when stacking accelerometers (which can monitor mass and resonance) on the processor chip, it is necessary to pay attention to the impact of external environment such as load and vibration on stress sensitivity, Henry said. "Encapsulating the accelerometer with silicone, RTV or other materials will insulate it from the package," he noted. However, a different bare sheet bonding technology needs to be developed later, because it should be noted that "it may try to use line bonding technology to connect with a pillow pad," Henry said. In addition, this will affect the reliability

"since you can't integrate all the functions on one silicon chip, you need to stack the bare chips to optimize the process," said markshaw, marketing, application and system manager of Freescale sensor product department. You can take advantage of high chip logic density and high withstand voltage without being limited by MEMS technology, he said. Henry believes that the sensor should be viewed from the perspective of packaging. The conclusion is that it is not placed on a single silicon chip, but on two chips, the processor and the sensor

shaw points out that the bare chip size of MCU chip with larger size is also larger. "MEMS has a high failure rate and a low yield," he pointed out that putting the processor and MEMS sensor on the same chip will pay a greater price. If the mens in the sensor area fails, the best processor will be scrapped

although it is also agreed that the yield of the sensor must be improved, frankcooper, President of ZMD USA, a mixed signal chip supplier, believes that it will be advantageous to turn to the simplified packaging provided by what he calls the "single silicon chip solution". This method has more advantages than the method of binding ASIC wires to sensors and connectors, and then packaging them together

"the real single-chip solution puts the G sensor (accelerometer), temperature sensor or flow sensor and the signal processing component on the same chip, so that the oil collector can be removed to achieve the minimum line bonding," Cooper said. As a result, there are fewer places where burst, short circuit, fatigue and pollution occur during sensor installation

safety and engine efficiency will still be the focus of current and future automotive sensor applications

when the tire contacts the road

because the sensors have to face the harsh environment they have never encountered before, reliability is also a problem. A representative application is tire pressure sensing (TPS). The national highway traffic safety administration of the United States mandated that 20% of new vehicles should be equipped with TPS sensors in the model year 2006

johnmcgowan, head of sensing and Control Department of Infineon technology, said that TPS sensors are used in "cramped and muggy places" and must be durable and long-life. In addition, they must have a reasonable cost. Infineon engineers developed such a sensor by placing a cmosasic for data processing and signal modulation and a piezoelectric pressure measuring element in a common lead frame. The "three-layer silicon sandwich" structure with ASIC sandwiched between two layers of glass is durable, McGowan said. Henry of Freescale also talked about the issue of "media compatibility". TPS sensors may be exposed to "interesting chemicals" and liquid can splash onto the tires in the garage. These things include: acid spilled from the battery, assembly lubricant, dust, chemical residues from the manufacturing process and wet air in the inflated tires

McGowan of Infineon said that integrating the processing function with the sensor can ensure the accuracy of temperature compensation, self-correction, failure mode detection and other functions. In terms of cost control, efforts can be made by integrating multiple functions and features on a single chip (contrary to the discrete passive components used in the past) and mass production. Finally, this intelligent attached sensor allows a smaller central processing unit to be freed from data operations for faster decision-making processing

the current tire pressure monitoring sensor is either installed outside the tire as a convex piece or fixed inside the rim. Because these devices are powered by button batteries, McGowan said that first-line suppliers pursue a battery life of 10 years. "To achieve this, we use vehicle information in our processing algorithm to reduce the sampling and transmission rate when the vehicle stops," he added

future pressure monitoring may be accomplished by sensors directly embedded in the tire structure. These sensors must be powered by what McGowan calls "energyscavening" technology, which uses tire flexibility to drive the strain devices (piezo) that provide energy to the sensors. The concept can be extended, for example, by using engine vibration as the working energy of the collision sensor. Another method is to drive the embedded tire pressure sensor from the outside of the tire by induction. The matters needing attention here include: the influence of any metal antenna ring in the tire hub on the physical characteristics of the tire

the latest dual chip accelerometer in QFN package has 6mm × 6mm × 1.45MM die stacking size (right)

The accelerometer core is on the top of the chip, and the CMOS control IC is on the bottom. (top) also shows QFN sensor stacking process

a group led by magnetimarelli around "smart tires "The initial anti-bacterial modified engineering plastics are a kind of plastics that can inhibit or kill bacteria, molds, alcoholomycetes, algae and even viruses contaminated on the plastics in the use environment. It goes beyond the simple level of pressure detection. The results of this group were presented at the sae2005 World Conference by andreaneponte, the project director, and pierodelapierre, the strategic innovation manager (paper) 。 Tire testing will not only test pressure; A three-axis accelerometer on the inner liner will also provide tire force data along the three axes, the size of the tire contact block, and road conditions (through vibration data)

although the battery was used in the test to ensure the reliability of the communication connection, the team believed that the strain gauge method could not provide sufficient power for the application in terms of the power level (300 MW) required by the sensor. Such a tire data system can be used to provide information for the vehicle chassis control system or determine whether tire or suspension system services are required

prospects for automotive sensors

in the next five years, other applications of sensors are likely to include more gyroscope based devices, said Shaw of Freescale. These devices will provide angular rate data for rolling stability control and other shaft closed-loop control. These gyroscopes will be based on MEMS. With the increase of production, the processing cost of MEMS will be reduced

peterknittl, marketing manager of Infineon's pressure and Hall effect sensors, believes that to enhance the performance of impact sensors triggered by airbags, pressure based devices will be used instead of the current g sensors. "This shift to 'active' sensors is driven by a new government decree (fmvss-201) to prevent side impact," he said. "When the structure is deformed, the G sensor will trigger. However, the pressure sensor in the door will detect a sound wave soon (about 5 to 6ms), while the detection time of the G sensor is 10ms." Future airbag systems may use both sensors at the same time to enhance redundancy

the development trend of automotive sensor system is not only the wind vane of where the sensor will be used, but also reflects "how various bus systems must work together and which application field each bus is dedicated to," ti's poppel said. Two wire or three wire

zmd Cooper said that he was surprised that the single line LIN bus has not been able to occupy a greater dominant position in the car. Typical applications still use a three wire radiometric sensor interface. Perhaps with the emergence of the new digital agreement, no one in the automotive industry wants to risk a recall or a bloody accident. " Therefore, the proven traditional devices will be handy for developers, and they hope to be able to easily use the inventory devices, he added. "Although the industry trend may be a digital interface, they still focus on analog (three wire) output signals."

cooper predicts that smaller, lighter and more powerful sensors will appear in the next five years, but only a few electronic control unit (ECU) modules will handle them. In addition, he believes that with fewer connections (lighter weight), fuel economy will be higher,Analysis of global architectural coatings market and development trend
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