The working principle and maintenance plan of the car computer board

The car computer automatically processes the input signals of various sensors according to a predetermined program, and then outputs signals to the actuators, thereby controlling the electronic devices in which the car operates.

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Classification of car computers

At present, automotive computers have been widely used, such as body computers, engine computers, transmission computers, and ABS computers. Although the number and types of computers configured on different models are not the same, the overall trend is to use one main computer to process the input signals of most sensors and to control other systems with smaller electronic control units.

Composition of car computer

The main part of a car computer is a single-chip microcomputer, which is a circuit board that integrates a microprocessor (CPU), a memory, and input and output interfaces. The microprocessor is the core component of the single chip microcomputer. The microprocessor converts the input analog signal into a digital signal, and compares and processes according to the stored reference data to calculate the output value. After the output signal is amplified by power, the actuator is controlled, for example, the injector. And relays, etc. With the increasing computing power and memory capacity of the single-chip microcomputer, the functions of the automobile computer are also increasing.

Car computer work process

(1) Signal filtering and amplification The input circuit receives input signals from sensors and other devices, and filters and amplifies the signals. The purpose of the input signal amplification is to increase the signal to a level that can be recognized by the car computer. Some sensors, such as oxygen sensors, generate a low voltage signal of less than 1V, which can only generate very small currents. Such signals are sent into the computer. The microprocessor must be amplified before, and this amplification is done by the amplifier circuit in the input chip of the computer.

(2) Analog-to-digital (A/D) conversion Since many sensors generate analog signals, and the microprocessor processes digital signals, it is necessary to convert analog signals into digital signals. This work is performed by a computer input chip. The number converter is completed. The analog-to-digital converter continuously scans the sensor's analog input signal at regular intervals and assigns a fixed value to the analog signal, which is then converted to a binary code. In some automotive computers, the input processing chip and the microprocessor are integrated.

(3) The microprocessor operates the signal that has been preprocessed and sends the processed data to the output circuit. The output circuit amplifies the digital signal and some of it is restored to an analog signal to drive the actuator.

As the degree of automation and automation of automobiles increases, more and more automotive computers will become more and more complicated. In order to achieve fast information transfer between multiple automotive computers, simplify circuits and reduce costs, communication systems must be connected to a network system using communication network technology. For example, the transmission needs to cooperate with the engine to automatically shift gears according to factors such as vehicle speed, engine speed and power load. Therefore, the transmission computer needs to obtain signals such as throttle position sensor, vehicle speed sensor, water temperature sensor and engine speed sensor. The transfer of information between the computer and the engine computer is usually done by the CAN bus.

Car computer features

(1) The car needs to travel under different roads and climatic conditions. The working environment of the car computer is poor, and it is often necessary to withstand vibration and changes in temperature and humidity. The power voltage of a car computer varies greatly, and it is also disturbed by electromagnetic waves inside and outside the car, so the car computer needs high reliability and durability to the environment.

(2) The car computer must be intelligent enough to have self-diagnosis and detection capabilities, to detect faults in the system in time, and to store fault codes, to inform maintenance personnel of possible faults in order to facilitate maintenance. For example, the airbag must be opened in a timely, correct and rapid manner at a critical moment, but most of the time the airbag is on standby, so the airbag computer must have self-checking capability to continuously confirm whether the airbag system is working properly.

(3) With a few exceptions, all car computers use a 5V power supply to drive their sensors. In the electronics industry, 5V voltage is almost universally accepted as a standard for transmitting information. This voltage is high enough for transmission reliability, low enough for the safety of computer chips, and the use of computer industry standard voltages, which make automotive parts manufacturing specifications and low cost for automakers.

Overhaul of car computers

The internal circuit of a car computer can be divided into two parts, namely a conventional circuit and a microprocessor including input, output, and conversion circuits. Conventional circuits mostly use general-purpose electronic components, which can be repaired if damaged. In actual use, most of the failures of automobile computers occur in conventional circuits. If you want to repair a car computer, you must first determine that it is a computer malfunction, so as not to blindly repair, causing unnecessary time waste and causing other circuit failures.

(1) Determining whether the computer is damaged The usual method for determining the damage of the computer is that the computer can not correctly output the control signal to drive the actuator when the relevant sensor signals can be input into the computer. Although this sentence is simple, it requires a lot of detailed and detailed basic inspection work. For example, the engine can not be started. After checking, it is determined that there is no frequency voltage on the injector plug when starting. When the relevant circuit is checked and the starting signal can be input into the engine computer normally, the computer does not output the driving signal to the injector, so that the engine computer can be determined. Internal failure.

(2) Find the damaged component according to the circuit. Find the corresponding computer terminal connected to the injector according to the circuit diagram or the actual line direction. Then use the digital multimeter's on-off gear to start from the determined computer terminal and search along the computer's printed circuit until Find a triode. This is because the computer usually uses a high-power triode to amplify the execution signal to drive the actuator, so the cause of such failure is mostly caused by a short-circuit of the triode that acts as a switch.

(3) Measuring the triode to determine the three poles of the triode. The pin corresponding to the printed circuit is the collector of the triode, and the thinner printed line next to it is the base. The confirmation method is to insert the porous plug of the engine computer, start the engine, connect to the printed wire to be confirmed using the voltage of the multimeter, and display the base of 5V. Test the triode with a multimeter. If the positive and negative resistances of the collector (c) and the base (b) are found to be infinite, the triode has been broken; if the resistance between the collector (c) and the emitter (e) is found to be zero , indicating that the triode has been broken down. In addition, it is necessary to measure other transistors and diodes connected near the transistor.

(4) Determining the triode for replacement There are several methods for determining the type of triode: 1 model. Check the model on the triode and determine the matching domestic triode through the triode correspondence table. 2 resistance. The base of the three-stage tube generally has a series of resistors, and the resistance value of the base is similar to that of the original transistor, and the resistance values ​​of the different colors are different. Because the base of the triode is controlled by the magnitude of the current, the computer voltage is fixed, so it is necessary to use the resistor to control the current. If the current is too large to burn the triode, the current cannot be triggered if it is too small. 3 measurements. Use the multimeter's diode to measure the properties of the triode. According to the characteristics of the triode, only one pin should be single-passed with respect to the other two pins. With this property, it can be determined that it is a triode. Only one pair of pins is a FET, and the other two tubes are opposite. The pin that the pin conducts is the base of the triode.

(5) When soldering the replacement triode to the circuit board, pay attention to solder as little as possible to avoid overheating. After the soldering is completed, use a multimeter to measure that the pins should not be connected to each other.

(6) Test the maintenance effect Connect the computer board to the wiring harness of the vehicle body under bare condition, start the engine to check whether the corresponding function is normal, and touch the triode by hand. Some heat is normal, if there is a problem with hot. Observe whether the fault light is on and perform a road test with a certain mileage.

The engine circuit controlled injector circuit is taken as an example to briefly explain the process of repairing the engine computer.

(1) Injector power circuit The injector circuit is divided into two parts: the power circuit and the engine computer control circuit. The fuel supply of the injector is mostly provided by the fuel injection relay. After the ignition switch is turned on, the fuel injection relay operates, and the battery voltage reaches the injector. At this time, the control signal of the engine computer is awaited to match the work required by the engine.

(2) Engine computer control circuit The engine computer calculates according to the load, the speed and various correction signals, and the output circuit outputs the injector pulse signal, and the drive circuit amplifies the voltage signal and then connects to the base of the NPN power transistor (b) ), the triode performs the switching operation of the pulse frequency, that is, the energization and disconnection of the injector electromagnetic coil is completed.

(3) Injector circuit fault analysis The control circuit for performing the injector switch action is to control the grounding circuit of the injector coil by the triode, the collector (c) of the triode is connected to the injector, and the emitter (e) iron. If the c-pole and the e-pole are short-circuited, there is a fault that the injector always sprays after the ignition switch is turned on; if the c-pole is disconnected, the injector cannot complete the grounding circuit, and the injector does not spray oil. In addition, if the protection diode connected in parallel with the c-pole of the triode is short-circuited, the injector will always spray oil.

(4) Injector circuit detection method can use tools such as digital multimeter, oscilloscope or LED test lamp. It is forbidden to plug and unplug the harness with power, or use pointer multimeter or high-power test lamp to avoid causing instantaneous large current to cause internal triode of engine computer. damage.

Connect the LED test light to the two sockets of the injector plug and turn the ignition on. If the LED light is always on, it means that the c-pole and the e-pole are short-circuited; if the LED is not lit, start the engine. If the LED is still not lit, it means that the c-pole and e-pole are open.

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