Smart sensors and modern automotive electronics

frozenviolet

Smart sensors and modern automotive electronics [Copy link]

1. Automotive Electronic Control and Safety System In

recent years, China's automotive industry has grown rapidly and has a strong momentum of development. Therefore, some experts in the commentary circle have predicted that the automotive industry may surpass the IT industry and become one of the most important pillar industries of China's national economy. In fact, the growth of the automotive industry will inevitably include the growth of IT industries related to the automotive industry. For example, although the value content of electronic products and technologies in FAW's products in China currently accounts for only about 10%-15%, the value content of electronic products and technologies in foreign cars is about 22% on average, and automotive electronics in mid- and high-end cars has accounted for more than 30%, and this proportion is still and continues to grow rapidly, and is expected to reach 50% soon.

Electronic information technology has become the dominant factor in the development direction of the new generation of automobiles. The improvement and improvement of various aspects of the power performance, control performance, safety performance and comfort performance of automobiles (motor vehicles) will rely on the perfect combination of mechanical systems and structures and electronic products and information technology. Experts in the automotive engineering community pointed out that the development of electronic technology has brought profound changes to the concept of automotive products. This is also one of the reasons why the electronic information industry has paid unprecedented attention to automotive electronics recently. However, it must be pointed out that, except for some in-car audio and video equipment, car communications, navigation systems, and in-car office systems, network systems and other in-car electronic equipment, which have undergone relatively little essential change, modern automotive electronics have entered a new stage of essential improvement from the applied electronic components (including sensors, actuators, microcircuits, etc.) to the architecture of in-car electronic systems. One of the most representative core components is the smart sensor (smart actuator, smart transmitter).

In fact, automotive electronics has gone through several stages of development: from circuit monitoring and control built with discrete electronic components, through independent, dedicated, semi-automatic and automatic control systems built with electronic components or components plus microprocessors, it has now entered a new stage of using high-speed buses (currently at least 5 or more buses have been developed and used), uniformly exchanging data of various electronic equipment and systems in the operation of the car, and realizing comprehensive and intelligent control. The new automotive electronic system consists of various electronic control units (ECUs), which can be independently controlled and coordinated to the best state of overall operation. For example, in order to keep the engine in the best working state, it is necessary to start with the measurement of the air flow and intake pressure of the inhaled cylinder, and then calculate the basic injection amount according to the working environment parameters such as water temperature and air temperature. At the same time, the throttle position sensor is used to detect the throttle opening to determine the engine working condition, and then control and adjust the optimal injection amount. Finally, the crankshaft angular velocity sensor is used to monitor the crankshaft angle and engine speed, and finally calculate and issue the best ignition timing command. This engine fuel injection system and ignition integrated control system can also be combined with the exhaust emission monitoring system and starting system to build an intelligent system that can maximize the power and torque of the automobile engine while minimizing fuel consumption and exhaust emissions.

Another example of safe driving can be given. For the purpose of smooth and safe driving, in addition to the use of a large number of pressure sensors and the general installation of anti-lock braking devices (ABS) for the control of only four wheels, many cars, including domestic cars, have added electronic power distribution systems (EBD). ABS+EBD can maximize the stability of driving in rainy and snowy weather. At present, some cars at home and abroad are further equipped with emergency brake assist system (EBA). In case of emergency, the system automatically detects the speed and strength of the driver's brake pedal and determines whether the emergency brake force is sufficient. If necessary, it will automatically increase the braking force. The self-control action of EBA must be completed in a very short time (such as one millionth of a second). This system can shorten the braking and sliding distance of a vehicle traveling at a speed of 200km/h by more than 20 meters. For the wheels, there is also an "electronic traction control" (ETC) system that monitors the speed of each wheel relative to the vehicle speed, and then distributes power to each wheel in a balanced manner to ensure that each wheel has a good balanced grip under harsh road conditions.

From the two examples listed above, it can be clearly seen that the development of automobiles has some basic requirements for automotive electronics:

1. The action of the electronic control system must be fast, correct and reliable. The technical approach of sensor (+ conditioning circuit) + microprocessor, and then through microprocessor (+ power amplifier circuit) + actuator can no longer meet the requirements of modern automobiles. It is necessary to ensure the correctness, reliability and timeliness of the control unit's action through hardware integration, direct data exchange and simplified circuits, and improve the degree of intelligence.

2. Now almost all mechanical structural components of automobiles are controlled by electronic devices, but the space in the car body is limited, and the space of the component system is extremely limited. The ideal situation is, of course, that the electronic control unit should be closely integrated with the controlled components to form a whole. Therefore, the miniaturization and integration of devices and circuits are an inevitable path.

3. The electronic control unit must have a sufficient degree of intelligence. Take the airbag as an example. It must be able to open instantly and correctly at critical moments, but the airbag is in standby mode most of the time. Therefore, the airbag ECU must have self-test and self-maintenance capabilities to continuously confirm the reliability of the normal operation of the airbag system and ensure that the action is "safe".

4. Various functional parts of automobiles have their own movement and control characteristics, and for electronic products, most of them are in very harsh operating environments, and they are different. Such as high temperature in working state, low temperature in static standby, high concentration of oil vapor and active (toxic) gas, as well as high-speed movement and high-intensity shock and vibration. Therefore, electronic components and circuits must have high stability, environmental resistance, self-adaptation, and self-compensation adjustment capabilities.

5. Equally important and sometimes even critical as the above requirements is that the electronic components and modules used in automotive electronic control units must be able to be mass-produced industrially and reduce costs to an acceptable level. Some microsensors and smart sensors are examples in this regard. For example, smart acceleration sensors can not only better meet the various needs of modern automobiles, but also because they can be mass-produced on the standard silicon process line of integrated circuits, with low production costs (several US dollars to more than ten or dozens of US dollars), they have found their largest application market in the automotive industry, which in turn has strongly promoted the electronic informationization of the automotive industry.

2. Smart sensors: a new generation of electronic devices that integrate microsensors and integrated circuits

Microsensors and smart sensors are emerging technologies that have only begun to develop rapidly in recent years. The technical names currently used in China's newspapers and magazines are still relatively vague. They are still generally referred to as sensors, or vaguely summarized as automotive semiconductor devices. There are also smart sensors (or smart actuators, smart transmitters) and microsystems, MEMS, etc. are all classified under the name of MEMS (micro-electromechanical systems). Here are the definitions and technical connotations of some commonly used technical terms in current European and American monographs.

First of all, it must be pointed out that in most cases, the sensors mentioned in the titles and full text of this article actually refer to three major types of devices: sensors that convert non-electrical input parameters into electromagnetic signal outputs; actuators that convert electrical signals into non-electrical parameter outputs; and transmitters that can be used as both sensors and actuators, among which the majority are transmitters that convert one form of electromagnetic parameter into another form of electromagnetic parameter output. That is to say, the technical characteristics of microsensors and smart sensors can be expanded and analogized to the physical dimensions of microactuators, microtransmitters-sensors (or actuators, or transmitters) with at least one physical dimension equal to or less than the sub-millimeter level. Microsensors are not simply the physical shrinkage of traditional sensors, but a new generation of devices based on semiconductor process technology: they use new working mechanisms and physical and chemical effects, use materials compatible with standard semiconductor processes, and are prepared using microfabrication technology. Therefore, they are sometimes also called silicon sensors. Microactuators and microtransmitters can be described by analogy with similar definitions and technical features.

It consists of two chips, one is the accelerometer unit (micro accelerometer) with self-detection capability, and the other is the interface circuit and MCU between the micro sensor and the microprocessor (MCU). This is an early (around 1996) but already quite practical device that can be used in the automatic braking and suspension systems of automobiles, and because the micro accelerometer has self-detection capability, it can also be used for airbags. From this example, it can be clearly seen that the advantage of micro sensors is not only the reduction in size, but also the convenience of combining with integrated circuits and mass production. It should mean that the use of this two-chip solution can shorten the design cycle and reduce the cost of small-batch trial production in the early stage of development. But for practical applications and the market, a single-chip solution is obviously more desirable, with lower production costs and higher application value.

Smart Sensor, Smart Actuator and Smart Transmitter - A device in which a micro sensor (or micro actuator, or micro transmitter) and some or all of its processing devices and processing circuits are integrated on a single chip (such as the single-chip solution of the micro accelerometer mentioned above). Therefore, intelligent sensors have certain bionic capabilities, such as fuzzy logic operations, active identification of the environment, automatic adjustment and compensation to adapt to the environment, self-diagnosis, self-maintenance, etc. Obviously, due to the requirements of large-scale production and reducing production costs, the design concept, material selection and production process of intelligent sensors must be as consistent as possible with the standard silicon planar process of integrated circuits. Some special processes can be added before the normal process flow, or during the process, or after the process is completed, but not too many.

In a package, a micromechanical pressure sensor is integrated with an analog user interface, an 8-bit analog-to-digital converter (SAR), a microprocessor (Motorola 69HC08), a memory and a serial interface (SPI) on a chip. The silicon pressure sensor at the front end is made using bulk silicon micromachining technology. The process of preparing silicon pressure sensors can be arranged before or after the integrated CMOS circuit process. The technology and market of this intelligent pressure sensor are mature and have been widely used in various pressure measurement and control units required by automobiles (motor vehicles), such as various barometers, nozzle front manifold pressure, exhaust gas exhaust pipes, fuel, tires, hydraulic transmission devices, etc. The application of intelligent pressure sensors is very wide, not limited to the automotive industry. At present, there are many manufacturers producing intelligent pressure sensors, and there are many varieties of products on the market, and fierce competition has emerged. As a result, the size of intelligent pressure sensors is getting smaller and smaller, and the peripheral connectors and discrete components required by the control unit are getting fewer and fewer, but the functions and performance are getting stronger and stronger, and the production cost is decreasing rapidly (now about a few dollars each).

By the way, it should be mentioned that in some Chinese materials, especially some product promotional materials, Smart Sensor (or device) and Intelligent sensor (or device) are generally referred to as intelligent sensors, but there are differences in European and American literature. Western experts and the public generally believe that Smart (intelligent) sensors have a higher level of wisdom and ability than Intelligent (knowledge-based). Of course, the connotation of knowledge-based is also evolving, but those devices that can only simply respond to environmental changes, make some corresponding compensations, and adjust the working state, especially those that do not require integrated processors, have too low a knowledge level and should generally not be classified as intelligent devices.

I believe that the most common smart sensor that most readers can often come into contact with is probably the CCD image sensor used in cameras, digital cameras, camcorders, and mobile phone cameras. This is a case where non-intelligent sensors are the only ones, because the electrical signal converted from light to each silicon unit in the CCD array is extremely weak, and must be directly and timely shifted and stored, and processed and converted into a standard image format signal. There are also more complex electronic and optical image stabilization systems equipped on mid- and high-end long-focal-length (IOX) optical magnification digital cameras and camcorders, especially the real optical image stabilization system in high-end products. Its core is a dual-axis or 3-axis micro-accelerometer or micro-gyroscope, which monitors the vibration of the fuselage and converts it into the displacement of each axis of the lens, thereby driving the movement of the variable-angle lens in the lens to keep the refractive optical path of the optical system stable.

Microsystem and MEMS (micro-electromechanical system) - a three-level cascade system consisting of microsensors, microelectronics circuits (signal processing, control circuits, communication interfaces, etc.) and microactuators, and devices integrated on a chip are called microsystems. If the device has micromechanical components such as mechanical linkage or mechanical actuators, it is called MEMS.

The left side of the MEMS chip gives the basic process technology required for the preparation of MEMS chips. The right side lists the main application areas. Obviously, the best solution for MEMS is to use materials and physical effects, design concepts and process flows that are compatible with silicon processes, that is, to use a combination of conventional standard CMOS processes and two-dimensional and three-dimensional micro-machining technologies, including the production of micromechanical structural parts.

The logical extension of microsensors is smart sensors, and the natural extension of smart sensors is microsystems and MEMS. The further development of MEMS is micromachines that can autonomously receive and distinguish external signals and instructions, and then independently and correctly act. At present, there are many types of MEMS that have been successfully developed and have commercial products, covering the major fields shown in Figure 4. Among them are two-dimensional and three-dimensional MEMS optical switches, which are one of the key components of all-optical optical communications and all-optical computers.

By controlling the micro-mirror array on the chip, the cross-connection of optical input/output is realized. This is the best mature solution for all-optical switching technology at present. The number of MEMS optical switches available on the market has reached 1296, and the switching time is about 20ms.

Micro-machines (also called nano-machines) are still in the development and testing stage, but many important laboratory products have emerged, such as the famous nano-motor, micro-insect, micro-helicopter and submarine. The technology industry generally believes that their successful development and practical application will have a profound impact on industrial technology and quality of life.