Application of MEMS Pressure Sensor in Automobile

The automotive electronic control system follows the basic logic of the conventional control system, including three links: perception, control, and execution. The sensor acts as a sensing unit for acquiring the system and environmental status. The control unit combines sensor input signals and control logic calculations to output control instructions, and the actuator completes the corresponding actions to form a closed-loop control.

According to the sensor category, there are many types of automotive sensors, including pressure, temperature, gas, acceleration, angle, position, speed, etc. In addition, new sensor subsystems such as cameras and radars are included.

Take the pressure sensor as an example, which is widely used in engine management systems, comfort systems, transmission systems, and safety systems. Among them, the MEMS pressure sensor occupies a major position in the medium and low-pressure range applications of 5~500kPa due to the characteristics of small size, high sensitivity, and low cost. MEMS pressure sensors generally realize signal sensing based on silicon, and realize small signal calibration, amplification, linearization and other processing of sensitive devices through signal conditioning circuits, and provide different signal output forms according to the needs of the back-end system. Usually, the realization of sensitive devices includes piezoresistive and capacitive in two ways. Piezoresistive type can realize different signal measurement methods including absolute pressure and differential pressure, while capacitive products are usually only suitable for absolute pressure signal measurement. This article focuses on typical applications of MEMS pressure sensors in automobiles.

Taking the engine management system as an example, the MEMS pressure sensors that will be used are shown in Figure 1, including: intake pressure sensor TMAP (1&2), turbo pressure sensor EGR TMAP (3), tail pressure difference sensor DPF/GPF ( 4), the pressure sensor of the oil tank evaporation leakage EVAP (5), the carbon canister desorption pressure sensor (6), the exhaust gas recovery system pressure sensor (7).

The typical structure of the intake pressure sensor is shown in Figure 2. The pressure range usually required is 10-115kPa, 10-250kPa and 50-400kPa, which are respectively used in naturally aspirated engines, turbocharged engines and exhaust gas recirculation with EGR Engine system, engine combustion needs to control the air-fuel ratio, and the intake pressure sensor is an important signal feedback of the combustion control system. It usually has high requirements for the accuracy of pressure detection and dynamic response time, and the output usually adopts 0~5V analog voltage Proportional output form, so that when the ADC in the ECU and the pressure sensor use the same VDD as the reference voltage, the error caused by the fluctuation of the power supply voltage VDD can be eliminated, and the power supply fluctuation is difficult to completely eliminate in the automotive electronic system.

In addition, with the trend of automotive electronics busting and the increase in the number and accuracy requirements of on-board sensors, SENT interface sensors are used more and more, especially in Powertrain systems. The SENT protocol was first initiated by GM and later became the SAE J2716 standard, and was widely used in automotive electronics. Because of its point-to-point, one-way transmission characteristics, it has a better cost advantage than CAN or LIN interfaces, does not require a dedicated transceiver, and has a good transmission speed. In addition, because of its single-wire form, the sensor only needs power, ground, and signal lines. The traditional analog voltage output sensor can be smoothly upgraded to the SENT output form. The wiring harness, pins, etc. are changed little, and there are more fault diagnosis and data. The transmission capacity will become the mainstream output form of the sensors of the powertrain system in the future.

Compared with ordinary ICs, in addition to the principle difference, the MEMS pressure sensor also has a very different application environment. Taking the intake pressure sensor as an example, it measures the physical quantity rather than the electrical quantity. The sensor needs a special package to introduce the changing air pressure into the On the MEMS sensitive membrane, and the automotive application environment determines that its atmosphere contains various potential water vapor and corrosive components, so it is necessary to coat a protective medium on the MEMS sensitive membrane to realize the transmission of pressure changes and protect the sensitive components from the environment. At the same time, it is necessary to ensure good accuracy performance and long-term reliability guarantee in the full temperature range and full pressure range. Generally, the working range of automotive MEMS intake pressure sensor covers -40℃~125℃. For some applications such as engines with exhaust gas recirculation EGR system, the intake port will contain exhaust components, which will bring higher temperature challenges and more Chemical components such as halogens, etc. are challenged by erosion.

The fuel tank evaporation leakage pressure sensor is an important part of the EVAP (Evaporative Emission System) of the fuel vapor management system, and its typical structure is shown in Figure 3. Fuel evaporation occurs in the fuel tank. Usually, an activated carbon canister is installed in the fuel system to adsorb oil and gas. At the same time, the activated carbon canister has a certain desorption pressure. Studies have shown that oil and gas evaporative emissions are the largest source of VOC emitted by automobiles, and the most important source of pollutants such as smog and PM2.5 in cities. The United States adopted strict standards for motor vehicle emissions earlier, and China’s “National VI” standards have further increased the requirements for emissions indicators, and fuel vapor pressure sensors and matching carbon canister desorption pressure sensors have become an inevitable choice.

Among them, the range of the carbon canister desorption pressure sensor is relatively small. Usually the range used by the ICE internal combustion engine system is -3.75kPa~1.25kPa. The measured value is the relative atmospheric pressure difference in the fuel tank, which means that the full range is only 5kPa. It is a gauge pressure measurement. Its small measurement range poses greater challenges to the performance, packaging and calibration of the MEMS pressure sensor itself, and because the application environment is in the fuel tank system, the sensor needs to be able to withstand corrosive media such as gasoline vapor and have a wide temperature range. Compensation ability. It also uses a carbon canister desorption pressure sensor, which has a measurement range similar to the TMAP intake pressure sensor, usually 115kPa absolute pressure.

The exhaust gas aftertreatment system is also the focus of the “National VI” standard. A series of sensors, actuators and control strategies have been added to further reduce emissions and improve combustion efficiency. A typical MEMS pressure sensor is a differential pressure sensor that monitors the state of a particulate matter trap. The particulate matter trap is called DPF on diesel engine systems and GPF on gasoline engine systems.

Taking the diesel engine system as an example, Figure 4 is a schematic diagram of the structure of a typical DPF tail pressure difference sensor. The differential sensor assembly has two air pipes on the structure, which are respectively installed with hoses and connected to the front and rear sides of the DPF trap. The internal structure realizes that the pressure difference between the two ends is reflected to the two sides of the MEMS sensitive diaphragm respectively.

When the DPF is blocked, the pressure difference between the front and rear ends will be very obvious. The typical range of the DPF differential pressure sensor is 100kPa, usually a proportional output analog voltage signal. The application environment of the sensor is relatively harsh, and the high temperature in the exhaust gas needs to be considered when designing And the influence of corrosive components on the sensor.

Nanocore NSPAS1 and NSPAS3 series of integrated pressure sensors are packaged in SOP8, integrated MEMS and ASIC, and are pre-calibrated before leaving the factory. The output curve can be flexibly configured to meet pressure sensors’ flexible needs in various applications. For harsh media, Nanochip can provide absolute pressure Pt platinum MEMS wafer NSP163X. NSP163X has extremely high reliability and media tolerance, and is an ideal choice for harsh media environments.

Nanocore Micro NSPGM series integrated gauge pressure sensor solutions can be flexibly applied to fuel vapor pressure gauge pressure measurement and DPF and GPF tail pressure difference measurement, and can be matched with differential pressure Pt platinum MEMS wafer NSP183X to meet the requirements of exhaust gas and oil and gas corrosive environments special requirements.

In addition to the above-mentioned fuel vehicle sensor applications, nanocore micro MEMS pressure sensors can also be used in HEV hybrid vehicles and BEV pure electric vehicles. For example, brake assist systems with start-stop functions and hybrid vehicles will use MEMS pressure sensors to detect vacuum. Therefore, MEMS pressure sensors can be used in new energy vehicles to detect the pressure of the battery pack for thermal runaway alarms.

In summary, Nanocore Microelectronics can provide a full range of solutions suitable for the above-mentioned multiple applications, including MEMS sensitive components, ASIC signal conditioning chips, and integrated sensor chips with compensation and calibration or customized modules. It can also provide a variety of interface ASICs such as precious metal MEMS that can withstand harsh media corrosion and SENT, LIN and other interface ASICs, as well as application-optimized flexible solutions to meet the demanding and high-reliability application requirements of automobiles. The high-performance copper series alloy materials launched by Shanghai Jinding New Material Technology solve the high-strength, high-reliability, heat-resistant, and related requirements of metal materials for automotive microelectronics. Welcome to discuss, negotiate, and cooperate.

Source: Shanghai KINMACHI New Material Technology organized from the Internet

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