Regarding the working principle of computers, I think most military friends are experts. It's a little tricky to say this This paper describes the working process of EFI engine from the cooperation of electronic control unit and sensor.
When it comes to sensors, it is actually a signal conversion device. Installed on all parts of the car. Its function is to detect the physical parameters under various working conditions in automobile operation and convert these physical parameters into electrical parameters that can be recognized by ECU. Then through the control and adjustment of ECU, the engine is controlled in the best working state. (All the sensors are basically mentioned before, and this post is not the point, so I will skip it here and talk about the relevant sensors when the ECU works. )
In this altar, we often understand ECU as the electronic control unit of the engine. In fact, ECU is not the electronic control unit of the engine, but depends on the different control objects. There are engine ECU, automatic transmission ECU, airbag ECU, ABS brake ECU, air conditioning ECU, anti-theft ECU and so on. By the way, you can't blame the old man for misleading in the future. The ECU of the engine is strictly EEC (Electronic Engine Control).
There are two kinds of sensor signals input to ECU:
1. analog signal; Such as water temperature, oil pressure, mixed gas concentration, etc.
2. Digital signals: such as speed, throttle position and crankshaft position.
Digital signals can enter directly, but analog signals must be converted into digital signals by A/D converter and then processed. The output of ECU is all digital signals, and the voltage is low, so it can't directly drive the actuator, so it is necessary to increase the output drive circuit. The output drive circuit is installed in the iron box of ECU, but it is not equal to the ECU chip. Most of them are discrete components and can be completely repaired. When replacing ECU at your own expense, you may wish to see whether to drive the circuit first. Including the chip, can be replaced (but the program must be entered). So we say ECU can be repaired, but the problem is that ordinary garage can't.
No matter what kind of gasoline engine, the best working state of the engine is adjusted by controlling the mixture concentration and ignition time. The electronic control unit ECU is also realized by grasping these two key points. Here I briefly introduce the basis of ECU programming.
We know that the air-fuel ratio when gasoline is completely burned to produce carbon dioxide and water is called theoretical air-fuel ratio; A/F = 14.7, where a is air quality and f is fuel quality; But actually burning one kilogram of gasoline is not the air quantity calculated theoretically. It is closely related to the engine structure and working conditions (temperature, load, etc.). ). So we take the theoretical air mass required to completely burn one kilogram of gasoline as the denominator, and the ratio of the air mass required to actually burn one kilogram of gasoline as the molecule is called the excess air coefficient λ, λ >; When 1 represents excess air, it is called lean mixture, λ.
The arithmetic unit in ECU constantly performs operations according to the data sent by the sensor, and takes the λ result as output control.
Because the engine can't be based on normal λ at different temperatures and different loads. At this time, the correction value was added when writing the initial program. For example; Change the A/F value to 2- 12 (provided by temperature sensor) when the cold car starts; Of course, when the hot car is running normally, the A/F value is the modified λ value with 14.7 as the target value (closed-loop control, open-loop control is 15. )
Taking λ result as output control, we often discuss how to control throttle opening and injector pulse width to adjust mixture concentration, so I won't go into details here.
In addition to the ignition time, the ignition time mainly refers to the first beat time and the late advance angle.
The first time is very simple. The missing tooth on the flywheel sends a signal to the ECU through the top dead center sensor (also called crankshaft position sensor), and then the crankshaft will send a signal to the ECU every 360 degrees. Therefore, ECU always knows the crankshaft position, and knowing the crankshaft position will know when the best ignition time is. The advance angle is calculated by ECU according to the engine compression ratio and intake air volume as a correction. In addition, the knock sensor will send out a voltage signal when knocking happens, and ECU will identify the cylinder position according to this voltage signal, and delay the ignition of the cylinder in time. Restore the engine to the best condition.
We often say that the yellow fault light is called the inspection engine of the EFI system.
Last week, the old Jiangsu army commander made a long-distance call and asked me, the light is on, can it be turned on again?
I told him that as long as the engine power and sound were normal, it would be fine to light it. Why? We know that the sensor of EFI system has been telling ECU to make corrections. But if the sensor fails, will the engine stop? I said no, because there is an alternative program in ECU called Home. For example, if the water temperature sensor is broken, the ECU takes the backup value of 80 degrees as the control parameter of fuel injection and ignition. So that the engine can continue to run. Reduce the probability of anchoring. Of course, at that time, the motivation and economy declined. You have to repair it in time, just like the water temperature sensor mentioned above is broken. If it is not repaired in time, it must be cooked.
Let's talk about the fault code after the alternative. The advantage of fault code is convenient maintenance. It is made up of several numbers. Looking up the table with these figures will clearly tell you what is broken and what to change. Anyone can fix it. The key is that you have a computer (self-explosion instrument) that can talk to ECU.
Fault codes can be divided into permanent fault codes (which can only be eliminated after maintenance) and temporary fault codes (sometimes no fault).
When a permanent fault code appears, the yellow fault light is always on, and when a temporary fault code appears, the yellow fault light is not always on, but it will be stored. The electronic control unit can store at most 15 fault codes. Some people say that when driving, it is often found that the yellow fault light is on and then off, which is the instantaneous fault code. For example, if the sensor is not in good contact, it is not that the sensor is broken. But it still left a short fault code. Even if there is no bad contact in the future, you have to wait for 50 starts to be eliminated. It is not like some people say that it can be eliminated by removing the battery and cutting off the power supply, because it is not the same as the concept of rest.
The initial program, correction program, replacement program and fault code are mentioned above, and the adaptive program is also mentioned.
The adaptive program is actually a memory that automatically records all kinds of records. Because there are errors in automobile manufacturing, assembly and adjustment; There are great differences in the degree of use and wear, but there are differences in the climatic conditions in the use areas and the driving habits of drivers. Therefore, an automatic correction program of "this driver, this engine" is added to the control software of ECU. Sometimes a big misoperation or drastic temperature change will make this program go wrong, and the yellow fault light should be on. The engine will also have such and such phenomena. At this time, the spectrum (adaptive result) stored in RAM can be disappeared by disconnecting the battery. When restarting, ECU will automatically give the initial value and correction value. Calibration time varies from five minutes to one hour. Due to the complexity, the working condition of the engine cannot be used as a basis within one hour after the battery is disconnected.
At present, there are many manufacturers of ECU, and the languages they use are different, so there is no unified fault code for each manufacturer, so they can only consult the manual. The initial procedure and correction value are related to the patent and confidentiality of technical data, so they are very mysterious.