Overview:
The entire structure of a car is complex, with tens of thousands of parts, but the basic structure can be broadly divided into four main parts: engine, chassis, body, and automotive electronics. The proportion of automotive electronics in the total vehicle cost has been steadily increasing, currently ranging from 15% to 30%, and for some high-end vehicles, it accounts for close to 40% to 50%. With the continuous development of intelligent technology, the development of other automotive modules has become more standardized; the comfort of a car is primarily reflected in the level of intelligence of its automotive electronics.
There are many automotive electronic systems, mainly including the vehicle power supply system, starting system, engine management system, lighting and headlight management system, instrument indicator system, air conditioning system, auxiliary systems, airbag system, automatic transmission electronic control system, electronically controlled suspension system, vehicle smart key system, parking assist system, vehicle entertainment system, vehicle telecommunication system, vehicle equipment wiring and vehicle bus system, etc. These systems combine to form the automotive electronic system.
Components of a car power supply:
The power system of a gasoline-powered vehicle mainly consists of a battery and a generator, while the power system of a dual-mode vehicle and a pure electric vehicle mainly consists of a power battery, a lead-acid battery, and a DC-DC voltage inverter. Power modules or power chips are then used within each system for voltage conversion. The main differences between the two are as follows:
1. The power system of gasoline vehicles is a low-voltage system, generally 12V. The power system of dual-mode vehicles and pure electric vehicles has both low-voltage and high-voltage power. The high-voltage power is generally 300V-500V or above, provided by the power battery; the low-voltage power is 12V, 24V and 42V, provided by lead-acid batteries or DC-DC voltage inverters.
2. In dual-mode vehicles or pure electric vehicles, the power battery is the power source of the entire vehicle, and the power battery supplies electrical energy to the electric motor to drive the vehicle; while the power of a gasoline vehicle is obtained by the engine burning gasoline, and it is not driven by electricity.
Since a car has multiple systems that are considered constantly powered, the lead-acid battery is needed to supply power when the alternator is not operating. This poses a significant challenge to both the battery and the electronic equipment, especially since the power consumption of the electronic equipment is a critical issue. Many manufacturers now require the static power consumption of the vehicle's constantly powered equipment to be less than 20mA, meaning that constantly powered systems themselves need to achieve a static power consumption of several mA.
In many cases, the system requires low voltage, necessitating voltage conversion of the lead-acid battery. This is especially critical when powered by a generator, where the interference immunity of the conversion power supply is critical. The alternating current generated by the generator is directly supplied to the system after only full-wave rectification; if the power supply filtering is inadequate, it can easily interfere with the internal systems. Currently, many vehicle safety systems generally use isolated power supplies for voltage conversion, while non-safety systems, due to cost constraints, use circuits built with non-isolated chips for voltage conversion.
Automotive electronic power supply environment and its requirements:
The application environment of automotive on-board power systems is more complex than that of ordinary power systems because the electromagnetic environment inside a car is much harsher. The electrical equipment in a car generates a significant amount of electromagnetic interference during operation. This interference has a wide frequency band and propagates into the power system through conduction, coupling, or radiation, thus affecting the normal operation of electronic equipment. The worst-case scenarios often involve interference generated by the vehicle itself, such as interference pulses from the ignition system, alternator, and rectifier system.
The most critical reason is that all the power supply in a car is connected to a single point, so interference between devices can cross-talk directly along the power lines and interfere with other devices.
Besides the internal interferences mentioned above, automotive electronics are exposed to much harsher external environments compared to other ordinary electronic products, especially factors such as temperature, humidity, vibration, rain, aging resistance, voltage fluctuations, and voltage surges. More importantly, as a commonly used means of transportation, the reliability and safety of automobiles are of paramount concern. The following is a summary of the temperature specifications for common automotive electronic components:
Table 1: Ambient Temperature Analysis for Automotive Electronic Systems
Electronic components must withstand severe environmental conditions. Since the Automotive Electronics Council (AEC) established quality control standards, the AEC-Q-100 chip stress test specification certification has provided strict control over automotive internal chips. AEC standards have gradually evolved into universal testing specifications for automotive electronic components. After more than 10 years of effort, AEC-Q-100 has become a universal standard for automotive electronic systems. Following AEC-Q-100, specifications such as AEC-Q-101 for discrete components and AEC-Q-200 for passive components were subsequently developed, along with guiding principles such as AEC-Q001, Q002, Q003, and Q004.
The ISO 16750 series of standards are environmental reliability standards for automotive electronics recently introduced by the International Organization for Standardization (ISO). These standards are commonly used in European vehicles and are gradually being adopted as national standards by various countries worldwide. They are also increasingly being referenced in company standards, becoming a widely used environmental reliability standard for automotive electronics. This series of standards comprises five parts:
Characteristics and requirements of electromagnetic compatibility in automotive electronics:
With the increasing variety of automotive electronic products and the replacement of many important monitoring and control system functions by electronic devices, the performance of vehicle safety has become closely linked to its operating electromagnetic environment. If the EMS capability of components is too low, internal or external electromagnetic interference can affect product performance to the point of directly impacting driving safety and causing personal injury. Due to the extremely high safety requirements of vehicles and their components, the EMC standards for vehicles are often several times more stringent than those for general electronic products.
EMS testing methods determine the immunity of a device under test (DUT) by applying external interference energy. Different interference energies require different testing methods and appropriate coupling modes to ensure successful coupling. The transmission paths of external interference energy are mainly divided into radiated and conducted types. Radiated interference refers to interference energy being transmitted through the air to the DUT or its lines (power and signal lines) without any transmission medium. Conducted interference, on the other hand, couples or injects interference energy directly onto the DUT or its lines via power or signal lines. The forms of external interference energy include continuous waves and transient waves, and are further divided into radiated and conducted coupling modes. Immunity testing methods can be subdivided into four main categories: continuous wave conducted, continuous wave radiated, transient conducted, and electrostatic discharge (ESD).
To address interference generated by automotive electronics themselves, the International Committee on Radio Interference (CISPR) has imposed stringent requirements on the automotive electronics industry, particularly for in-vehicle radios, digital televisions, and navigation devices, which are major sources of such interference. Therefore, CISPR 25: Limits and Test Methods for Radio Interference Characteristics for Protection of Vehicle Receivers, provides clear classifications for the emission status of automotive electronics. The EMS test items are as follows:
For electric vehicles, there are some special requirements: In addition to meeting the surge and pulse group requirements of GB/T 17626 series, the high-voltage part of electric vehicle electronics also has GB 13837 (Measurement methods and implementation levels of electric and magnetic field strengths of electric vehicles), which is a special standard specifically for the self-emissions of electric vehicles.
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