With the development of electronic technology and the increasing electrification of automobiles, traditional mechanical systems are finding it increasingly difficult to solve certain problems related to automotive functional requirements, and are therefore gradually being replaced by electronic control systems. Sensors, as key components of automotive electronic control systems, directly affect system performance due to their quality. Currently, ordinary cars are equipped with approximately dozens to nearly a hundred sensors, while luxury cars have even more. These sensors are mainly distributed in the engine control system, chassis control system, and body control system. Engine Control Sensors There are many types of engine sensors, including temperature sensors, pressure sensors, rotation sensors, flow sensors, position sensors, concentration sensors, and knock sensors. These sensors are the core of the entire automotive sensor system. They can improve engine power, reduce fuel consumption, reduce emissions, and detect faults. Because they operate in harsh environments such as engine vibration, gasoline vapor, sludge, and water splashes, their environmental resistance specifications must be higher than those of general sensors. Their performance requirements are numerous, with measurement accuracy and reliability being the most critical. Otherwise, errors in sensor detection will ultimately lead to engine control system malfunctions or failures. (1) Temperature sensor: mainly detects engine temperature, intake gas temperature, coolant temperature, fuel temperature, catalytic converter temperature, etc., and converts them into electrical signals to control the opening time and duration of the injector needle valve, so as to ensure the best air-fuel mixture is supplied to the engine and achieve exhaust purification effect. The temperature sensors used in practice are mainly wire-wound resistor type, thermistor type and thermocouple type. Wire-wound resistor type temperature sensor has high accuracy, but poor response characteristics; thermistor type sensor has high sensitivity and good response characteristics, but poor linearity and low applicable temperature; thermocouple type sensor has high accuracy and wide temperature measurement range, but amplifier and cold junction treatment issues need to be considered. (2) Pressure sensor: mainly detects cylinder negative pressure, thereby controlling ignition and fuel injection; detects atmospheric pressure, thereby controlling air-fuel ratio during hill climbing; detects cylinder internal pressure, thereby controlling ignition advance angle; detects exhaust gas recirculation flow, engine oil pressure, brake oil pressure, tire air pressure, etc., and reacts to the relevant quantities. There are several types of automotive pressure sensors, among which the most commonly used are capacitor type, piezoresistive type, differential transformer type (VDT), and surface elastic wave type (SAW). Capacitor type sensors have the characteristics of high input energy, good dynamic response, and good environmental adaptability; piezoresistive type is greatly affected by temperature and requires a separate temperature compensation circuit, but is suitable for mass production; LVDT type has a large output and is easy to digital output, but has poor vibration resistance; SAW type has the characteristics of small size, light weight, low power consumption, high reliability, high sensitivity, high resolution, and digital output, and is a relatively ideal sensor. (3) Rotary sensor: mainly used to detect crankshaft angle, engine speed, choke opening, vehicle speed, etc., thereby controlling ignition advance angle, fuel quantity and injection time, etc. The main products include generator type, magnetoresistive type, Hall effect type, optical type, vibration type, etc. (4) Oxygen sensor: detects the air-fuel ratio in the exhaust and sends a negative feedback signal to the fuel supply system to correct the injection pulse and adjust the air-fuel ratio to the theoretical value to achieve the ideal exhaust purification effect. Zirconia and titanium oxide sensors are commonly used. (5) Flow sensor: measures the intake air volume and fuel flow to control the air-fuel ratio. There are mainly air flow sensors and fuel flow sensors. The air flow sensor detects the amount of air entering and controls the amount of fuel injected by the electronic fuel injector to obtain a more accurate air-fuel ratio. The products used in practice are mainly Kalman vortex type, vane type and hot wire type. The Kalman type has no moving parts, is sensitive and has high accuracy; the hot wire type is easily affected by the pulsation of intake gas and is prone to wire breakage; the fuel flow sensor is used to detect the fuel flow rate to calculate the fuel consumption of the car. The products are mainly waterwheel type and ball circulation type. (6) Knock sensor: detects the vibration of the engine and adjusts the ignition timing appropriately according to the detected knock signal. The main products are magnetostrictive type and piezoelectric type. Chassis Control Sensors Chassis control sensors refer to sensors distributed in the transmission control system, suspension control system, power steering system, and anti-lock braking system. They have different functions in different systems, but their working principle is the same as that of sensors in the engine. The main types of sensors are as follows: (1) Transmission control sensors: mainly vehicle speed sensors, acceleration sensors, engine load sensors, engine speed sensors, clutch sensors, water temperature sensors, oil temperature sensors, etc. The information obtained by these sensors is processed to enable the electronic control device to control the shift point and torque converter lock-up, thereby achieving maximum power and maximum fuel economy. (2) Suspension system control sensors: mainly vehicle speed sensors, throttle opening sensors, acceleration sensors, vehicle height sensors, steering wheel angle sensors, etc. The system automatically adjusts the vehicle height based on the information detected by these sensors, suppresses changes in vehicle posture, and achieves control over vehicle comfort, handling stability, and driving stability. (3) Sensors for power steering systems: These mainly include vehicle speed sensors, engine speed sensors, torque sensors, etc. These sensors enable the power steering electronic control system to achieve easy steering, improved response characteristics, reduced engine wear, increased output power, and fuel savings. (4) Anti-lock braking sensors mainly utilize wheel angular velocity sensors to detect wheel speeds. When the slip ratio of each wheel is 20%, the brake fluid pressure is controlled to improve braking performance and ensure vehicle handling and stability. Sensors for vehicle body control: The main purpose of using these sensors is to improve vehicle safety, reliability, and comfort. Their requirements for harsh environment resistance are not as strict as those for engine and chassis sensors. Generally, industrial sensors can be applied with slight modifications. These mainly include various temperature sensors, air volume sensors, and sunlight sensors used in automatic air conditioning systems; vehicle speed sensors in brake and door lock systems; acceleration sensors in airbag systems; light sensors in brightness control systems; ultrasonic sensors in blind spot alarm systems; and image sensors. Trends in Automotive Sensor Research and Development Due to the importance of sensors in electronic control systems, the competition among advanced automobiles is, in a sense, a competition of sensors. Countries worldwide place great emphasis on theoretical research, new material applications, and product development in this field. Diamond possesses excellent heat resistance and high thermal stability; carbonization only begins on its surface above 1200℃ in a vacuum and above 600℃ in the atmosphere. Utilizing this characteristic, thermistors suitable for high temperatures can be fabricated, enabling temperature monitoring and control within a range from room temperature to 600℃. These sensors are suitable for use in harsh environments with high temperatures and corrosive gases, exhibiting stable performance and long service life, and can be used for high-temperature measurements in engines. Furthermore, diamond has a high deformation rate at high temperatures, which can be used to fabricate vibration and acceleration sensors for use in high-temperature environments. Combined with other materials for vibrating membranes, they can be used as high-temperature, corrosion-resistant, and highly sensitive pressure sensors for vibration detection and measurement of engine and cylinder pressure. Fiber optic sensors are gaining widespread attention due to their strong anti-interference capabilities, high sensitivity, light weight, small size, and suitability for telemetry. Currently, many mature products have been launched, such as fiber optic torque sensors, as well as sensors for temperature, vibration, pressure, and flow. While developing and utilizing new materials, the advancements in microelectronics and micromachining technologies are driving sensors towards miniaturization, multifunctionality, and intelligence. Miniaturized sensors utilize micromachining technology to integrate micron-sized sensing elements, signal conditioners, and data processing devices onto a single chip. Due to their small size, low cost, and ease of integration, they can improve system testing accuracy. For example, integrating miniature pressure and temperature sensors allows for simultaneous pressure and temperature measurement, and the temperature effect in pressure measurement can be eliminated through on-chip computation. Many miniature sensors are already available, such as pressure sensors, accelerometers, and silicon accelerometers for collision avoidance. It is said that embedding miniature pressure sensors in car tires can maintain proper inflation, preventing over- or under-inflation, thus saving up to 10% on fuel. Multifunctionality allows sensors to simultaneously detect two or more characteristic parameters. Intelligent sensors, equipped with dedicated computers, possess intelligent characteristics. Furthermore, sensor response time, output interface with computers, and other issues are also important research topics. With the development of electronic technology, the technology of automotive sensors will inevitably become more sophisticated.