1.1 Introduction to Automotive Sensors
Automotive sensors are an indispensable part of automotive electronic control systems. They measure information such as position, pressure, torque, temperature, angle, distance, acceleration, and airflow, and convert this information into electrical signals as inputs to the automotive electronic controller. The accuracy and reliability of the sensors directly affect the control performance of the automotive electronic control system.
Figure 1: Schematic diagram of some automotive sensors
Sensors are primarily used in three main areas in automobiles: powertrain, chassis, and body & safety and comfort. There are many types of sensors, and the variety is constantly expanding. Due to the complex operating conditions and high reliability requirements of automobiles, sensors are required to operate normally in temperatures ranging from -40℃ to 125℃, with an error range within 1%, while also being cost-effective for widespread application.
Figure 2: Three major application areas of automotive sensors
The application of automotive sensors is becoming increasingly widespread, expanding from initial engine sensors to chassis, body, and other areas, with their quantity and variety constantly increasing. Automotive sensors can be categorized by the physical quantity measured: pressure sensors, temperature sensors, flow sensors, speed sensors, acceleration sensors, etc. They can also be categorized by their working principle: physical sensors, chemical sensors, and biological sensors. Sensors generally consist of a sensing element and a conversion element, requiring them to sense the measured quantity and convert it into a usable electrical signal according to a certain rule. Sensors need good sensitivity, accuracy, and dynamic response characteristics.
Figure 3: Structure diagram of common rail pressure sensor
Automotive sensor industry:
Preliminary estimates suggest that ordinary passenger cars typically have dozens of sensors, while high-end vehicles can have hundreds. According to a report by market research firm Strategy Analytics, global automotive sensor shipments reached 2.19 billion units in 2010, and are projected to reach 5.5 billion units by 2020, representing a compound annual growth rate of approximately 10%, higher than the growth rate of global car sales during the same period.
Figure 4: Global Sensor Market Size (100 Million Units)
Among the major application areas of automotive sensors, powertrain sensors are used the most due to increasingly stringent fuel consumption and emission regulations, in order to improve fuel efficiency and reduce carbon emissions. The second largest category is safety assistance sensors, which are experiencing the fastest growth. Given the traffic safety regulations introduced by various countries and the trend of intelligent connectivity, the market prospects for safety assistance sensors (cameras, millimeter-wave radar, etc.) are expected to be broad.
Figure 5: Several types of safety auxiliary sensors
According to a report by market research firm Strategy Analytics, the global automotive sensor market is projected to grow at a CAGR of 6.8%, from $16.9 billion in 2012 to $23.5 billion in 2017. Automakers' plans to improve vehicle safety, emissions, and fuel economy will drive the global automotive sensor market size to exceed $25.2 billion by 2020.
Figure 6: Global Sensor Market (USD Billion)
As a type of high-precision component, automotive sensors face stringent requirements at every stage, from research and development to manufacturing. Automotive sensor manufacturers need strong technological R&D capabilities and supply chain management skills. Currently, leading global automotive sensor companies include Bosch, Continental, Sensata, Infineon, Honeywell, TRW, and Delphi. These companies have broad sensor product lines, leading technologies, and numerous customers, creating a high barrier to entry in the automotive sensor market.
Figure 7: Panoramic View of the Sensor Industry Chain
Looking further ahead, the automotive sensor market is divided into many sub-markets, with slightly different leading companies in each sub-market, presenting a market landscape where each company has its own strengths.
The domestic automotive sensor market is basically monopolized by foreign companies, with leading domestic automotive sensor companies including Goertek.
Driving factors in the automotive sensor industry:
1. Drivers of demand for powertrain system sensors: Increasingly stringent fuel consumption and emission regulations require powertrain systems to meet the requirements of low emissions and improved fuel economy. At the same time, consumers' pursuit of excellent driving control has prompted the use of a large number of sensors in powertrain systems and the continuous improvement of the performance of related sensors.
2. Drivers of demand for chassis system sensors: safer driving, the trend of lightweight vehicles, and the introduction of safety regulations such as collision avoidance systems (e.g., AEB) and tire pressure monitoring have accelerated the widespread application of speed sensors, gyroscopes, millimeter-wave radars, cameras, tire pressure sensors, and vehicle height sensors.
3. Drivers of demand for vehicle body system sensors: Consumers' increasing emphasis on comfort and convenience in purchasing vehicles, as well as the increasingly sophisticated passive safety systems (front, rear, and side collision sensors, rollover sensors, occupant sensing sensors, etc.).
4. Moore's Law: Moore's Law is a very important driving force in the electronics industry. Performance doubles every 18 months. Automotive electronics will benefit greatly, as it can provide better electronic control systems and high-performance automotive sensors.
Development trends: intelligentization, integration, and sensor fusion
Technology Trends:
1. Integration trend: Using semiconductor manufacturing technology and micromachining technology to manufacture sensors, achieving sensor integration, facilitating large-scale mass production of sensors, and reducing sensor costs.
2. Intelligentization trend: Combining sensors with microprocessors enables sensors to simultaneously perform detection, signal processing, and communication functions, thereby improving the reproducibility, adaptability, and reliability of sensors.
The most commonly used sensor categories in automobiles are pressure, temperature, gas, and motion sensors. These sensors are increasingly evolving towards MEMS sensors, which are becoming a driving force for growth in the automotive sensor market. Simultaneously, due to the collaborative operation and integration of various automotive electronic systems, information from different sensors requires comprehensive processing, making sensor fusion an unstoppable trend.
(1) MEMS is an important development direction for automotive sensors
MEMS (Micro-Electro-Mechanical System) sensors are developed based on semiconductor manufacturing technology. They integrate microcircuits and micromechanics on a chip according to functional requirements, enabling a MEMS system at the millimeter or micrometer level to have precise and complete electrical, mechanical, and optical characteristics.
MEMS sensors commonly used in automobiles include pressure sensors, accelerometers, and gyroscopes. These three types of sensors are also among the most mature MEMS devices, and their market growth is primarily driven by the growth of the automotive and consumer electronics markets. In the future, with the trend towards integrated systems and the development of MEMS-related devices, more and more types and quantities of MEMS sensors will be applied to automobiles. As MEMS technology matures and costs decrease, more and more MEMS sensors are being used in automobiles.
MEMS Market Landscape: Bosch leads in MEMS technology and products, leveraging its deep expertise in the automotive sector to achieve a significant market dominance. Following closely are STM, TI, and Avago. Leading Chinese MEMS manufacturers are AAC Technologies and Goertek. Bosch, Denso, Honeywell, and Analog Devices (ADI) also have broad product lines in automotive MEMS sensors.
(2) Sensor fusion trend:
Different sensors have their own advantages and disadvantages. The high safety and reliability requirements of automotive electronic control systems necessitate a certain degree of redundancy. Therefore, leveraging the strengths of different sensors and integrating them for collaborative operation has become an important safety design approach. We know that millimeter-wave radar exhibits significant advantages in speed measurement and adverse weather conditions, but its measurement range and resolution are slightly lower. LiDAR, on the other hand, can complement the strengths of various sensors (as shown in the table below), making sensor fusion a growing trend.
2.1 Introduction to Commonly Used Sensors
2.1.1 Pressure Sensor
Semiconductor pressure sensors: Pressure is applied to a silicon diaphragm, which contains a piezoresistive element manufactured using micromachining techniques. The sensor and signal processing circuitry are typically housed within the same housing. They are very compact and easy to assemble and layout. Reverse assembly techniques are commonly used to attach the measured pressure to the sensor chip.
2.1.2 Speed Sensor
There is a difference between absolute rotational speed and relative rotational speed in space. An example of absolute rotational speed is the yaw rate (yaw speed) of a car about its axis, which is essential for vehicle dynamics. Examples of relative rotational speed are the speeds of the crankshaft and camshaft, and wheel speeds (used in ABS/TCS), which are mainly measured using an incremental sensor system (containing a gear and a speed sensor).
Electromagnetic induction sensors utilize the relative motion between a conductor and a magnetic field to generate an induced electromotive force, making them a type of electromechanical energy conversion sensor. These sensors are characterized by simple circuitry, stable performance, low output impedance, and a wide frequency response.
2.1.3 Temperature Sensor
Temperature measurements on a car are almost entirely based on the sensitivity of thermistor materials to temperature changes. These resistive materials have positive (PTC) and negative (NTC) temperature coefficients. Converting the thermistor's changes into an analog voltage is done almost entirely with the help of an additional resistor that is temperature-neutral or inversely sensitive.
2.1.4 Millimeter-wave radar
Millimeter-wave radar is a high-precision sensor used to measure the relative distance, relative velocity, and azimuth of objects, and is a key component supporting safe driving. Millimeter-wave radar mainly comes in pulse and continuous-wave types. Continuous-wave radar can be further divided into CW (Constant Frequency Continuous Wave), FSK (Frequency Shift Keying), PSK (Phase Shift Keying), and FMCW (Frequency Modulated Continuous Wave), among others. FMCW radar is the most commonly used millimeter-wave radar.
The FMCW radar system mainly includes transceiver antennas, radio frequency front-end, modulation signal, and signal processing module. Millimeter-wave radar achieves target detection range, azimuth, and relative velocity through correlation processing of received and transmitted signals.
Millimeter-wave radar can work in all weather conditions. Compared with other sensors, millimeter-wave radar has obvious advantages in speed measurement and adverse weather conditions. It is used in systems such as ACC, AEB, and FCW and is known as the "eyes of the car".
