Behind the improvement of IQ of the hottest car

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Behind the improvement of automobile "IQ"

for many years, sensors used to measure pressure, temperature and acceleration have been the protagonists of automotive electronics. However, a large number of systems that need to have such functions, such as fuel injection control, fuel economy and safety systems (including "smart" airbag and tire pressure monitoring), have gone beyond placing a sensor where it is needed and sending the sensing signal back to the control unit. The export growth of China's extruder products will show a level of steady progress

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. But 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 require strict speed, but focus on simplicity and low cost, such as seat positioning, checking the damage of parts, and temperature control. Single wire Lin also means lighter weight, resulting in better fuel economy

Matthias poppel, 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 work of the central processor of the system. But he went on to say that the reliability of electromechanical sensors that integrate machinery and electronics is a problem. "Its flexibility is not enough (for design engineers), because such integrated sensors may only have one supplier, while components combined by discrete devices are generally from several suppliers," 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, he said, PCB equipped with Mechatronic sensor attached to a measuring device must be tested and verified to ensure stability and reliability under any expected action, load, temperature and vibration conditions

Steve Henry, 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 sensor accelerometers is that users want the integrated sensor and controller IC to have a smaller package."

henry said Freescale provided a 6mm × 6mm QFN 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 processor chips, we need to pay attention to the impact of external environment such as load and vibration on stress sensitivity, Henry said. "Wrapping the accelerometer with silicone, RTV or other materials will insulate it from the package," he said. But then a different bare sheet bonding technology needs to be developed, because "it may try to use line bonding technology to connect with a pillow pad," Henry said. In addition, this will also affect reliability

"since you can't integrate all functions on one silicon chip, you need to stack the bare chips in order to optimize the process," said Mark Shaw, marketing, application and system manager of Freescale sensor products department. You can take advantage of high chip logic density and high withstand voltage (sensor processor) 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 silicon chip, but on two chips, processor and sensor

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

although we also agree that we must improve the yield of sensors, Frank Cooper, 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 minimum wire bonding can be achieved," Cooper said. As a result, there are fewer places where burst, short circuit, fatigue and pollution occur in the installation of the sensor

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 model year 2006

John McGowan, head of the sensing and Control Department of Infineon technology, said that TPS sensors are used in "cramped and stuffy places", and must be durable and long-lived. In addition, they also have a reasonable cost. Infineon engineers developed such a sensor by placing a CMOS ASIC for data processing and signal modulation and a piezoelectric pressure measuring element in a common lead frame. The "three-layer silicon sandwich" knot of ASIC is sandwiched between the two layers of glass. 9. Column spacing: 460mm; The structure is strong and durable, McGowan said

Henry of Freescale also talked about the problem of "media compatibility", in which TPS sensors may be exposed to "interesting chemicals" and liquids can splash on the tires in the garage, including acid spilled from the battery, assembly lubricants, 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 functions such as temperature compensation, self-correction and failure mode detection. In terms of cost control, efforts can be made by integrating multiple functions and features on a single chip (contrary to the way of discrete passive components used in the past) and mass production. Finally, this kind of intelligent auxiliary sensor allows the smaller central processing unit to be liberated from data calculation, so as to make faster decision 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 the 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 "energy scavenging" technology, which uses tire flexibility to drive the strain devices (piezo) that provide energy to the sensors. This concept can be extended, for example, using engine vibration as a collision sensor to generate low activity free radicals to slow down the working energy of combustion. 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 bare chip 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 the QFN sensor stacking process

a group led by Magneti Marelli has carried out initial work around "smart tire", which goes beyond the simple level of pressure detection. The results of this group were published at the Sae 2005 World Conference by Andrea neponte, project director, and Piero de la Pierre, Strategic Innovation Manager (paper) 。 Tire testing will not only test pressure; A triaxial 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 believes that the strain gauge method cannot 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

Peter knittl, the marketing manager of Infineon's pressure and Hall effect sensors, believes that in order to enhance the performance of the impact sensor triggered by the airbag, pressure based devices will be used instead of the current g sensor. "This shift to 'active' sensors is driven by a new government decree (fmvss-201) to prevent side impacts," he said. "When the structure is deformed, the G sensor will trigger. But the pressure sensor in the door will detect a sound wave soon (about 5 to 6ms), and the detection time of the G sensor is 10ms." Future airbag systems may use both sensors at the same time, thereby enhancing 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 all kinds of bus systems must work together and which application field each bus is dedicated to," ti's poppel said

two wire or three wire

zmd's Cooper said he was surprised why 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 use the inventory devices conveniently, 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 the reduction of connections (lighter weight), fuel economy will be better

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