Business information author: Wuji 2022-10-27 21:07: 5810 Read 0 comments.
As we all know, the characteristics of automobile electrical system are low voltage, DC, single-wire system and negative tension. Low voltage refers to the safe voltage whose electrical system voltage is 12V or 24V and lower than 36V. Direct current means that automobile batteries, generators and electrical appliances all use direct current. One-wire system means that all electrical appliances in the car can be controlled by a positive wire. Negative electrode refers to all the power supply and electrical equipment in the car, and their negative electrodes are directly connected with the car body as the public circuit of the electrical system.
Low voltage, DC and single-wire systems are easy to understand. Some are for safety, and some are to reduce the cost and complexity of the system, but why do we have to use negative reinforcement? Can't you use a positive tension material?
In fact, when cars were first invented, they were made of iron for a long time. That is to say, the anode of the power supply and electrical appliances is directly connected with the vehicle body, and the cathode is connected with the cathode of the power supply through wires. However, with the increase of automobile electrical components, people soon found a problem-serious corrosion of automobile body, and this corrosion has nothing to do with the corrosion resistance of automobile steel plate. After careful study, automobile engineers found that the root of the disease lies in the positive electrode of the electrical system, and the electrochemical corrosion rate of the car body steel plate will be faster. Subsequently, the technicians changed the electrical system of the automobile to a negative electrode and grounded it, which greatly reduced the degree of electrochemical corrosion. Since then, all automobile electrical systems have adopted negative pole iron, which has become an international standard.
So, why does the use of cathode iron accelerate the corrosion of the car body? Let's analyze the problem briefly.
First, let's look at the principle of car body corrosion. The car body is all steel plates, and the basic component is iron. Iron is also an active metal, which reacts with oxygen and water in the air at room temperature. Iron atoms lose their outer electrons and become iron ions, which combine with oxygen to form hydrated iron oxide, also known as rust. This is the root cause of automobile body corrosion. Obviously, the faster the iron atom loses electrons, the faster the automobile will corrode, and the greater the degree of corrosion. This corrosion process is essentially a tiny galvanic cell composed of iron, oxygen and water, so it is also called electrochemical corrosion.
In order to prevent the car body from corrosion and slow down the car body corrosion rate, various anti-corrosion measures such as galvanized steel plate, electrophoresis, painting, waxing of cavity and so on were adopted in the automobile production process. The main purpose is to block the contact between iron, oxygen and water, and also make the car body have great anti-corrosion ability. But the car body can't be 100% isolated from air and water. Because it is necessary to keep the metal bare in some parts. For example, the grounding point of each electrical component. In addition, when the bolts are tightened, the separator will also be damaged. So many cars are prone to rust where they brake, which is the reason.
Then, how do the positive and negative sides of the automobile electrical system affect this corrosion process and corrosion speed? Try to analyze them separately.
First of all, let's look at the working principle of the battery, the power source of the car. Almost all the batteries in cars are lead batteries, the positive plate is lead dioxide, the negative plate is pure lead, and the electrolyte is dilute sulfuric acid. The lead on the positive plate exists in the state of lead ion, and the lead on the negative plate exists in the state of ionization. That is to say, lead ions and electrons are formed, and there is a potential difference of about 2. 1V between the positive and negative plates. This is the basic principle of electromotive force generated by storage battery. The charging and discharging process of storage battery is actually the mutual transformation process of lead, lead dioxide, lead sulfate, sulfuric acid and water, in which the current is formed with the flow of electrons.
The positive pole iron is added to the electrical system of the car, and the body and the positive pole of the battery are connected together. Lead in the positive electrode of battery exists in ionic state, and the metal activity of lead is not as good as that of iron. In this case, the electrons in the car body will continue to be adsorbed on the battery. When the iron atoms in the car body lose electrons, they will become iron ions, and when they meet water and oxygen in the air, they will quickly combine with hydrated iron oxide and corrode. Therefore, the application of positive iron will improve the activity of car body metal, which is prone to electrochemical corrosion, so the car body corrosion is faster and more serious.
What if it is reinforced with a negative electrode, that is, the body is connected to the negative electrode of the battery? Watch it again. There are free lead ions and electrons on the negative plate, and the potential is-0.1v. In other words, the electrons on the negative plate are abundant. In this case, the negative electrode of the battery can provide electrons to the car body steel plate at any time, that is, it is difficult for the car body steel plate to lose electrons and be oxidized. Just like "passivating" metal by changing its shape, electrochemical corrosion of the car body is not easy to occur, and the corrosion of the car body will be reduced. At present, there are also machines that adopt anti-corrosion measures of attaching active metals to metal shells, and the principle is actually the same.
Therefore, the negative grounding method can effectively avoid and slow down the electrochemical corrosion of the car body, so that the car body has better corrosion resistance. This is the most fundamental reason why the car hangs the negative side rail. An interesting phenomenon is that in 1950s and 1960s, cars produced in China basically used cathode iron. At that time, the slogan was "the east wind overwhelms the west wind", so what we did was different from that in the west. They made negative steel, we made positive steel, they made alternators, and we made DC engines, so the cars of that era could not be replaced by domestic electrical parts. However, it was later found that this did not conform to scientific principles, and it was gradually revised after the 1970 s. This also shows that science has no national boundaries and ideological problems.
In addition, there are phenomena that confuse many people. Commonly used cars are generally difficult to rust, but cars that have been parked for a long time will soon rust. This is called "water does not rot, cardinal does not rot." In fact, this phenomenon is also related to the electrochemical corrosion of the car body. In ordinary cars, current flows through the body at any time, and the metal of the body can get electrons at any time, so it is not easy to be oxidized and corroded, and the process of oxidation and corrosion slows down. When the car is parked for a long time, after the battery is dead, there is no current in the car body, and the electrons supplied in the car body metal will also decrease. If oxygen and water destroy the antirust layer of the car body, the steel plate of the car will be further corroded and the steel plate will be oxidized and rusted. This is the main reason why parking is easy to rust.
The electrical system of a car is single-wire and the negative electrode is iron, so many electrical equipments only need to install their metal shells directly on the car body. If the shell is non-metallic, pull out the wires and connect them to the car body. Such a line is called a turnout. Theoretically, all electrical equipment needs a switch, but in order to reduce the number of switches on the car, the negative poles of many electrical equipment are connected together and connected to the car body through a male conductor. This conductor is a public switch.
Turnouts play a very important role in automobile lines. If the turnout is rusty or loose, the resistance in this part will increase greatly. This is like a car circuit with a large resistor in series, which makes it difficult to start the car, the lights are dim and the signal is inaccurate. Therefore, iron wire is also called the "lifeline" of automobile electrical system. Many electrical faults of automobiles are caused by poor cable contact. When we remove the electrical fault of the car, we should first check whether the cable is corroded or loose. This can greatly reduce our workload and shorten the inspection time.
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