Difference between digital signal and analog signal of automobile electronic control system

At present, ECU is not only used in engines of some mid-to high-end cars, but also can be found in many other places. For example, anti-lock braking system, four-wheel drive system, electronically controlled automatic transmission, active suspension system, airbag system, multi-directional adjustable electronically controlled seat, etc. Are equipped with their own ECU. With the improvement of automotive electronic automation, ECU will increase day by day, and the circuit will become more and more complicated. In order to simplify the circuit and reduce the cost, a technology called multi-channel communication network is adopted to transmit information between multiple ECU on the vehicle, and the ECU of the whole vehicle forms a network system, that is, CAN data bus. The purpose of editing this paragraph is mainly used in the following aspects: 1. Engine control, ignition, valve timing adjustment, throttle adjustment, starting motor adjustment, starting clutch adjustment, fuel injection adjustment, etc. 2. Continuously variable speed control, belt position adjustment and speed adjustment 3. Automatic gearbox control, relay or electromagnetic directional control 4. Active suspension, adjustment of air spring stiffness and damping hole size 5. Driving force and anti-skid control, including: ABS anti-lock braking system EBD electronic braking force distribution EBA emergency braking auxiliary device ESP electronic driving comfort system TCS tracking control system MSR engine resistance moment control EDS electronic differential system OBD vehicle-mounted automatic diagnosis system DSC dynamic stability control system 6. Body control BCM, including window lifting (including force sensing-safety), sunroof folding and sliding, seat lifting adjustment, wiper, defroster, etc. 7. Air conditioning, heating and ventilation control, including compressor, condenser, evaporator fan, expansion valve, etc. 8. Electronic switches and lighting, including headlights, taillights, display backlight, acceleration and deceleration, radio, CD, etc. 9.ACC electronic active cruise control 10. Airbag self-diagnosis and ignition control 1 1. Self-diagnosis of active seat belt. Pull-back seat belt ignition control 12. EPS steering control, HPS steering control 13. TPC tire pressure control 14. Automobile instrument 15. Theft alarm 16. Tail height balance system 17. The intelligent sensor, that is, the sensor with ECU, is 18. Other electronic control units in this section are generally composed of CPU, extended memory, extended IO port, CAN/LIN bus transceiver controller, A/D D/A converter (sometimes integrated in CPU), PWM pulse width modulation, PID control, voltage control, watchdog, heat sink, and other electronic components. ECU with specific functions also includes infrared transceiver, sensor, DSP digital signal processor, pulse generator, pulse distributor, motor drive unit, amplification unit, strong and weak current isolation and other components. The whole circuit board is designed and installed in an aluminum box, which can be easily installed on the body sheet metal by buckles or screws. General ECU adopts general CPU function integration and is easy to develop. The software is generally written in C language, which provides a rich library of drivers and functions, including programmers, simulators, simulation software and calibration software. Bosch, Delphi, Denso and VDO of Chinese mainland are all leaders in the automotive ECU industry. Edit the specific function of this paragraph. The electronic control unit is the core control element of the electronically controlled gasoline injection system. It is actually a microprocessor. Its function is to receive the signals from various sensors, complete the processing of these information, and send corresponding instructions to the executive parts, so that the engine performance, fuel consumption and exhaust emissions are in the best state. The specific functions of the electronic control unit are as follows: ① Fuel injection control calculates the basic fuel supply according to the air intake and speed of the engine, and corrects it according to the information such as pressure and temperature, and sends fuel injection instructions to the fuel injectors. (2) Exhaust purification control automatically adjusts the fuel supply and accurately controls the air-fuel ratio according to the signal of the oxygen sensor in the exhaust pipe. ③ Ignition control According to the engine temperature and load, the optimal ignition advance angle is calculated. (4) Idle speed control controls idle speed according to water temperature, air temperature and loads of various accessories. ⑤ Other controls include pressurization, cold start, detonation, exhaust gas recirculation, cylinder change, speed limit, automatic speed change control and automatic diagnosis. The role of the electronic control unit in this paragraph has been edited. Electronic control unit (ECU) is the core of electronic control system. It is installed on the rear plate of the right front wheel cover of an automobile, and is mainly composed of a microprocessor, a program memory, a power supply circuit and various interface circuits. After the whole vehicle is powered on, ECU starts to detect the standby sensor and switch signals regularly, and based on this, it calculates the optimal fuel supply, optimal ignition timing and optimal idle speed of the engine under various working conditions. Through the output drive circuit, the fuel injector, ignition assembly, idle DC motor and air conditioning system are controlled. The ECU will also detect the functions of various components in the electronic control system at any time. Once the fault is found, the fault source is immediately stored in the designated unit of ECU in the form of code, and whether the system enters the "limping" state is judged according to the fault type. At the same time, let the "engine fault warning light" light up to warn the driver to repair as soon as possible. Editing the test of this electronic control unit is usually considered as a work that will not add value. This is true in an ideal world, because in an ideal world, there will never be defects in the production process, the system design will never be defective, the software will always run normally, there will never be customer returns, and the quality problems of products and raw materials will be zero. Because there will be no fault, testing is unnecessary. But the world is not perfect, and it needs to pass the test to reach the minimum quality standard of measurability, repeatability and traceability. Quality does have value, although its value cannot be directly measured. The necessity of testing is also reflected in other aspects. Automobile manufacturers have their own quality requirements and standards (such as QS-9000) and long-term tracking and supervision requirements. Automobile manufacturers usually require parts suppliers to send their parts to B&; A) Test the components before the factory (the components are assembled into a complete vehicle). B& amp； Factory A is a labor-intensive factory. It is unacceptable to rework the car due to the supplier's component failure, which will cause great losses. Supplier contracts usually include penalty clauses related to component defects caused by suppliers. ECU manufacturers need to prove that their products meet the customer's specifications, which needs to be achieved through DV (Design Verification) testing. Manufacturers also need to prove that their production process can produce products correctly, which needs to be achieved through PV (production verification). Quality standards usually require quality evaluation of a certain proportion of ECU to ensure that there are no defects in the production process. This quality assessment is conducted through continuous consistency (small-scale design verification) testing. Other ecus edited in this paragraph are engine control system and engine control unit, which is the full name of ECU, and ECU is used to manage the engine. Every car will have this little thing. Whether you drive a Mercedes-Benz BMW Fit QQ is an important part of the engine. There is no difference between good and bad, and it does not affect the performance and price of the whole vehicle. However, if it is to be modified, especially for cars with turbines, the modified ECU can improve the performance by about 50%. How to modify ECU will be explained in detail in future articles. Before 1967, the fuel supply system of gasoline engine was supplied by carburetor, which is completely different from today's EFI engine. Carburetors use the pressure difference before and after the throttle to absorb oil, which not only can not accurately control the fuel supply, but also restricts the improvement of automobile power and environmental protection performance. The working feature of EFI system is "quantitative and timing" fuel injection. How much fuel the engine needs and when to inject it are directly related to the engine speed, air flow and other parameters such as water temperature and oil pressure. How to deal with so many parameters and send injection instructions to the injection system? This requires the intervention of engine control unit, and ECU comes into being. Simply put, ECU is like a home computer, which consists of processor CPU, I/O interface, A/D converter and storage unit ROM+RAM. It's just that the CPU of ECU can't achieve high-speed processing like our computer. The main frequency of an automobile ECU is only 10KHz. Now even high-performance ECU can't reach the processing speed of home computer. I/O interface is equivalent to computer monitor, mouse and keyboard, and is used to "communicate" with the processor. Of course, this is only the communication between machines, and ordinary car owners rarely have the opportunity to communicate with ECU. A/D converter is the premise of ECU. It can convert the received sensor signal into data for running in ECU. So how does ECU work? Simply put, it is a command process: "thinking", "directing" and finally "confirming". "Reconnaissance" is completed by sensors, which are responsible for "reconnaissance" of the whole engine. On an engine, there are dozens of large and small sensors. Throttle opening sensor, crankshaft speed sensor, oxygen sensor, crankshaft position sensor, camshaft position sensor, air temperature sensor, water temperature sensor and knock sensor are the most basic sensors in automobile engines. Sensors are everywhere. They are responsible for collecting relevant information and transmitting it to ECU in the form of electrical signals. After the A/D converter converts it into a digital signal, the ECU judges the working state of the engine through operation, which is the "thinking" process of the ECU. And what is the standard of the process of "thinking"? A computer can't think, but what it needs is a program stored in ROM. This is equivalent to a software. When the data is transmitted to ECU, the existing data of ROM program is compared with the collected signal, and ECU obtains the adjustment method. This program is the soul of ECU, and the programming of this program is based on a large number of experimental data, which often needs bench test and road test to be established. Of course, ECU is not static. RAM can record the data of car driving. Usually, many ecus have the ability of "learning". ECU can learn the driver's driving style from the data recorded in RAM, which is more humanized. Of course, once a fault occurs, you can also read information from RAM to support maintenance. After completing the "thinking", the next thing the ECU needs to do is "command". The injector is controlled by ECU, which is responsible for adjusting the injection quantity and injection time, and the gasoline pump is responsible for supplying oil to it; Both the ignition controller and the ignition coil are controlled by ECU. After that, ECU needs to receive data again to confirm the end of closed-loop control. The above is the working principle of ECU, although the current ECU is not as powerful as a computer. But there is a saying that the future ECU will be a powerful computer system, which will integrate engine, automatic gearbox, ABS system, car entertainment audio-visual system, four-wheel drive torque distribution system, active suspension system, airbag+seat belt system and so on. We can enjoy the car audio-visual system, play computer games and receive GPS signals. The coolest thing is that you can implant Schumacher-style driving mode into your engine, or you can choose Raikkonen-style driving. Even more exciting, it is said that Microsoft has started feasibility analysis. Let's wait and see.