Now, the preventive safety of vehicles is increasingly valued, and MEMS sensors are applied in many areas of automotive safety technology. Below is a summary of the top ten applications of MEMS sensors in the automotive field:
The Electronic Stability Control System (ESC) is a device used to prevent vehicles from skidding on wet roads after rain or on curved sections. This device uses an acceleration sensor from Murata Electronics Oy (hereinafter referred to as MFI).
Typically, relying only on ABS and traction control systems cannot meet the safety requirements for vehicles on curved sections. In this case, the Electronic Stability Control System (ESC) can control the vehicle to prevent it from deviating from the road by correcting understeering or oversteering in the driver’s operation. This system uses a gyroscope to measure the vehicle’s yaw angle while using a low-gravity acceleration sensor to measure lateral acceleration. The measured data is then compared with the results obtained from the vehicle’s speed and wheel tilt angle to adjust the vehicle’s steering to prevent skidding.
The acceleration sensor is usually independently installed near the vehicle’s center of gravity or installed on a printed circuit board as part of a sensor group in the form of a mounted component. The standard measurement range is ±1.5 to 2.0g; the offset is independent of temperature or usage time, stabilizing below 100mg; the frequency band is within the range of 0 to 50Hz.
The Electronic Stability Control System (ESC) typically needs to be detected laterally to ensure that the influence is minimized when subjected to longitudinal acceleration or vehicle deceleration. When installing MFI’s acceleration sensor on a printed circuit board, two installation orientations can be selected: whether the detection axis is parallel or perpendicular to the mounting surface. If using an independent acceleration sensor, the corresponding bracket needs to be selected based on the installation position.
Globally, the standard regulations for ESC are actively being promoted. Under the framework of the United Nations “World Vehicle Regulations Coordination Forum” and the “1998 Agreement,” the global technical regulation (GTR) for “Light Vehicle Electronic Stability Control Systems” was completed in 2008 and approved by WP29 (i.e., GTR8). Countries and regions including the United States, Europe, Japan, Australia, and South Korea have already made or are in the process of making ESC a mandatory safety device. As a signatory to the “1998 Agreement,” China has fully participated in the coordination process of the ESC global technical regulations since 2007, proposing several proposals based on domestic ESC product development, application, and testing capabilities, and is currently formulating relevant national standards.
EPB (Electronic Parking Brake) replaces traditional parking brake devices based on mechanical levers and chains, providing drivers with more effective parking assistance. Also, by eliminating the parking brake lever between the driver and passenger seats, the space around the driver’s seat can be utilized more effectively. The EPB system can continuously adjust the braking force according to the vehicle’s longitudinal tilt. Just press the corresponding button on the dashboard to lock the brakes; when the vehicle starts and accelerates, the brakes will automatically unlock.
This system can also assist in controlling the vehicle during low-speed traction to prevent the vehicle from rolling backward on a slope. After interfacing with the distance sensor system signal, it can even complete parallel parking in narrow areas. If integrated with the engine anti-theft system, it can form one of the most reliable anti-theft mechanisms.
The actual measurement starting point of the sensors in this system is usually within ±3°; the corresponding gravity acceleration value is about 50mg. This aligns perfectly with the offset stability requirements throughout the vehicle’s lifespan and temperature range. The frequency range of internal sensors is kept as low as possible, with an upper limit not exceeding 10-50Hz.
In four-wheel-drive vehicles, since each wheel may slip, the parameters required for the vehicle speed and wheel speed for the ABS system cannot be measured by sensors. Therefore, the vehicle’s acceleration/deceleration information can only be obtained by measuring the forward and backward acceleration. The acceleration sensor used in the ABS system can be installed either as an independent component or integrated on the printed circuit board within the ABS controller, and can also be installed within other sensor types.
The measurement range of the acceleration sensor used in the ABS system is typically between 1 to 2G (G being the acceleration due to gravity). The error offset must remain below 100mg throughout the detection temperature range and the vehicle’s lifespan. The direction of the detection axis of this sensor must be in the forward and backward direction of the vehicle. The acceleration sensors from Murata Electronics Oy can meet the application needs for various sensor units and printed circuit board mountings.
The main purpose of the Electronic Control Suspension System (ECS) is to adjust the suspension system based on information such as driving speed, road conditions, steering situation, and gear state, providing drivers with good operational stability and ride comfort. The ECS system presents users with various driving experiences, from smooth and gentle to high-speed excitement. The driver can freely switch between sporty, normal, and comfortable driving modes by simply pressing a selection button.
The internal acceleration sensors of the ECS system can be used to detect the vehicle’s motion state and sometimes to detect the vertical motion state of the front wheels. Two acceleration sensors used to detect the vehicle’s motion state are installed near the fixed points of the front shock absorbers and springs. The acceleration sensor near the wheel hub is installed in the area close to the shock absorber and wheel spring. This allows the measurement data from the two groups of sensors to calculate the vertical distance difference between the vehicle body and the wheels. In more advanced hub sensor systems, acceleration sensors are replaced by distance sensors to directly measure the distance between the wheel and the vehicle body.
Additionally, many ECS systems have an extra acceleration sensor installed in the middle or rear of the vehicle to detect vehicle bumps, which can slightly reduce the tilt of the vehicle during acceleration or deceleration.
Air suspension systems are now used in most mid-to-high-end and luxury vehicles, including sport utility vehicles (SUVs). By adjusting the volume of air in the tanks at the corners of the vehicle body, the suspension settings can be corrected. This system typically includes one special gas compressor, one to two gas storage tanks, four shock absorber units made up of air springs and traditional dampers, two to five independent acceleration sensors, and an electronic control unit (ECU).
Due to the high cost of air suspension systems for mid and small-sized vehicles, suspension systems that replace air with oil are often used. Although the systems that adjust oil quantity are cheaper, they cannot achieve the efficiency and comfort of air suspension systems. The adjustment of oil quantity is achieved by special electronic valves, and this system will use three to five independent acceleration sensors.
As part of vehicle stability control, the Anti-Roll Stability Control System (ARC) is typically integrated into the Electronic Stability Control System (ESC) or suspension system. Anti-roll control can prevent the vehicle body from swaying significantly during the activation of the braking device or abnormal actions of the stabilizer. When integrating the ARC system into the ESC system, an additional acceleration sensor for detecting the vehicle’s forward and backward acceleration (with a measurement range of 1-2g) is required.
When this system is used in vehicles such as SUVs or off-road vehicles with a higher overall body or suspension position, it may also be designed as a standalone system. In this case, an independent sensor needs to be installed on the top of the vehicle, while another is installed at a corresponding position on the lower floor.
The anti-vibration control of engines and transmissions is attracting more and more attention from industry professionals. One important reason is that the new generation of engines can save fuel by shutting down some cylinders without operating at full load.
The shutdown of individual cylinders in the engine can lead to vibrations in the vehicle body. Moreover, relative to the weight of the engine, the weight of the vehicle body is becoming lighter. Especially for diesel-powered six-cylinder or eight-cylinder engines, the vibrations from the engine can cause the entire vehicle to vibrate. For hybrid vehicles, the frequent switching between gasoline and electric engines can also lead to body vibrations, which is particularly prominent in small diesel hybrid vehicles.
The latest solution to address body vibrations is the active electronic control damping device. These devices use acceleration sensors in closed-loop control systems (feedback control systems) and are installed in various critical parts of the vehicle body.
HAS (Hill Start Assist) is an electronic parking brake system directly connected to the main braking device and ESC system. When the vehicle starts on a slope, it can automatically control the braking pressure to prevent the vehicle from sliding backward.
The HAS system requires high-performance sensors to detect slight tilts in the vehicle’s forward and backward direction, which is the slope of the road. The stability requirement for the sensors is that the angle measurement error within the lifespan and temperature range is less than 3° (equivalent to a sensor output value of about 50mg). All “offset errors” generated during vehicle assembly can be eliminated in the final “offset calibration” step on the production line; additionally, the completed offset signals can also be calibrated through the software installed in the electronic control unit (EUC) within the electronic stability control (ESC) system.
Heartbeat detection refers to a new system that detects whether there are people inside the vehicle when the vehicle is locked and should be in an empty state, using high-sensitivity sensors and precise computer software in coordination. This system can be used to detect children left in the car due to parental negligence or illegal intruders hiding in the vehicle.
The principle of vehicle anti-theft devices and engine lock anti-theft devices is to use relatively inexpensive two-axis acceleration sensors to detect the vehicle’s motion state. If combined with high-precision heartbeat detection sensors, it can form a more secure advanced anti-theft system.
The rollover sensor, also known as the rollover detection sensor, is integrated into the airbag control system as part of the passenger protection system. Specifically, the rollover sensor consists of one-axis or two-axis (roll angle and pitch angle) angular velocity sensors and acceleration sensors, used to detect the angular velocity and acceleration in the vertical direction (Z-axis) of the vehicle. The measurement range of the acceleration sensor in this system is generally 3 to 5g, with a maximum frequency band not exceeding 400Hz, and a stable offset of about 300mg.
The application of pressure sensors in the automotive field for tire pressure monitoring systems is rapidly advancing. Although this system primarily illuminates warning indicators by monitoring the internal air pressure of tires, if linked with various vehicle safety systems, it can achieve many attractive functions beyond just tire blowout warnings. When tire pressure is abnormal, the following issues may occur:
Low pressure in the front tires will lead to understeering, while low pressure in the rear tires will lead to oversteering.
Whether tire pressure is insufficient or too high, it will significantly shorten the tire’s lifespan.
When the tire pressure deviates from the optimal value by 0.4bar, the tire lifespan will be reduced by 30%; in cases of insufficient pressure, for every 0.6bar drop in pressure, fuel consumption will additionally increase by 4%.
When driving at speeds exceeding 100km/h, if tire slippage occurs, the tire will detach from the road, which is extremely dangerous.
When tire pressure is lower than 50% of the normal value, even with the ABS system, the braking distance when driving at 100km/h on wet roads will increase by 10m.
When tire pressure falls below a certain value, the system will issue an alarm.
Abnormal tire pressure will hinder the normal operation of the suspension system.
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