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1. Introduction
Automobile circuit wire harness is an important channel for connecting automobile electronic components. With the development of modern automobile manufacturing technology, the number of circuit wiring harnesses is increasing. When the circuit cable harness spontaneously ignites, some braking functions of the automobile will fail, and the corresponding automobile will be out of control easily. It may cause the car to catch fire, and these two performances have great potential safety hazards for the moving vehicles, so they must be improved. It also shows that the analysis topic in this paper has practical significance.
2. Causes of Auto Circuit Harness Spontaneous Combustion
2.1 Overload Factors
In the process of automobile driving, the circuit harness will be in the state of power overcurrent. In this state, there may be two situations in the circuit harness, namely, the temperature of the circuit harness will increase continuously due to power overcurrent. If it is kept in this state for a long time, the temperature of the circuit harness will reach a higher level, and the power overcurrent performance of the harness will decrease. If the over-current voltage exceeds the over-current performance of the circuit wiring loom itself, both cases are overload phenomena. Then, under overload condition, first of all, too high temperature will lead to the spontaneous combustion of the circuit harness, and secondly, under the condition of high over-current voltage, it will lead to short circuit, and the corresponding circuit harness will have a large resistance, which will also generate huge temperature and cause spontaneous combustion.
2.2 Factors of Closed Loop
Closed circuit is a common circuit connection method among automobile circuit harnesses, that is, the connection between electrical equipment and wires. Under normal closed circuit, the circuit harness will generally not spontaneously ignite. However, according to the actual performance, under some special conditions, the internal current of the circuit harness will directly enter the wires without passing through the electrical equipment, which means that the closed circuit is abnormal, and it is easy to cause power failures such as short circuit, which will correspondingly cause the circuit harness to spontaneously ignite.
2.3 Fuse Factors
Fuse is the protection facility of circuit harness. Under the protection of fuse, the over-current performance of modern automobile circuit harness is very high. Under this condition, if the fuse fails, the circuit harness will lose its protection, and a series of problems will easily appear. The fuse failure usually shows that the wire diameter of fuse wire in fuse is inconsistent with the wire, which should be improved during rectification. In addition, the fault performance of the fuse also includes the fuse displacement, that is, when the car is running, the vibration caused by kinetic energy will impact the fuse, and accordingly, if the fuse is not stable enough, it will be displaced, resulting in corresponding power failure and spontaneous combustion.
3. Auto Circuit Harness Spontaneous Combustion Rectification Method
3.1 Overload Test and Rectification
Because there are many causes of automobile overload, it can't be generalized in the rectification. This paper will choose a conventional factor as the experimental basis. The overload factors selected in this paper are: a large number of electrical equipments are connected in the closed circuit Wiring Harness, which leads to excessive current and voltage on the wiring harness, which leads to overload phenomenon. The current and voltage in this overload phenomenon is 1 ~ 6 times higher than that in the normal state. Therefore, this paper will also select this data as the experimental basis to keep the wiring harness in this state for a period of time, and confirm that it will lead to the spontaneous combustion of the wiring harness. In this paper, the corresponding parameters are set in the conventional automobile system, and then the test work is carried out on this basis. The purpose of the test is: when the circuit harness is overloaded, only the connected electrical equipment will be abnormal, while other electrical equipment will not be affected. Therefore, the overload position can be located, and then the equipment can be rectified. The test preparation, methods and results will be analyzed below, and the rectification methods will be put forward.
3.1.1 Test preparation
Modern conventional automobile products are adopted. On the premise of permission, the technical documents of this product are consulted, and the cell circuit diagram, pin definition, Connector pin schematic diagram, function specification and whole vehicle circuit schematic diagram of related manufacturers are analyzed, and the test list is compiled accordingly. On this basis, this paper selects digital oscilloscope, DC stabilized voltage source, electronic load, oscilloscope, current test probe, data acquisition equipment, fuse wires of different specifications, wiring harness and electrical box as research instruments, and at the same time, according to the corresponding methods, the equipment is arranged and connected, and it is confirmed that the test can be carried out normally through simple tests.
3.1.2 Test Methods
Firstly, according to the test list data obtained above, disassemble the loaded equipment in the test object on this basis. At this time, the load will be recalculated, and the unloaded equipment will be connected to the loop accordingly. Secondly, for the lap joint of the test object, the positive electrode of the battery is connected to it, and a load device is placed between the connecting lines, and a short connector is placed in the device, so as to achieve the purpose of load control. Finally, the load of the harness is increased by the load equipment, so that the internal electronic load exceeds 135% of the upper limit of the fuse, and the temperature of all loop nodes is detected accordingly.
3.1.3 Test Results
Because the equipment affected by overload phenomenon is fuse, the data obtained in this paper will be put forward in the fuse rectification method later, and there is no significance for rectification here.
3.2 Closed Loop Test and Rectification
The self-ignition phenomenon of circuit harness caused by closed circuit is very serious, which can easily lead to fire. Therefore, in order to avoid this phenomenon, our company, Kable-X, will set up the whole vehicle circuit for the test object, and on this basis, carry out the bench short circuit test. This part of the test preparation, test methods, results and rectification methods will be analyzed below.
3.2.1 Test Preparation
In the closed-loop test, firstly, the above-mentioned overload test preparation contents are configured, which will not be described here. Secondly, a digital oscilloscope, a DC voltage stabilizing source, a notebook computer, a data collector, fuse wires of various specifications, a set of wiring harnesses and electrical boxes, as well as vehicle wiring harnesses, electrical boxes, batteries, lap joints, etc. are configured. Then, they are connected according to the corresponding methods, and it is confirmed that they can run normally through simple tests.
3.2.2 Test Methods
The closed loop test method is as follows: according to the test list, connect the DC regulated power supply with the automobile generator to form a closed loop; Directly connecting the DC regulated power supply with the storage battery terminal to form a closed loop; The acquisition equipment is used to connect the two closed circuits, and then the computer equipment is used to collect the data, and the abnormal phenomena in the test are controlled. Check the schematic diagram and circuit diagram of the whole vehicle system in the test list, and monitor the problems of all fuse wires to form a test data table; Confirm whether the wire diameters of all fuse wires are correct; Confirm the specification of the short-circuit conductor, and according to relevant theories, its length is at least 10cm, and its width is more than 30% of the original conductor of the test object; Before each short-circuit test, test the loop state first. If there is current, you can start the test. Otherwise, you need to apply current first, and then remove the fuse. At this time, the loop will run without fuse. You can know the loop load problem by observation.
3.2.3 Conclusion and Rectification Methods
The test results show that under the condition of no fuse, the rated value of closed loop is too large, which leads to the increase of current output, the smaller width of loop diameter, the easy accumulation of current to form a larger resistance, and the longer loop length, which leads to the increase of current output. On the basis of the test results, aiming at the closed loop problem, it should be rectified by reducing the rated value, increasing the loop diameter and reducing the length of the harness.
3.3 Fuse Influence and Rectification Methods
Combined with the above 2.1, the influence of fuse can be confirmed. Therefore, this part will not test the fuse, and directly introduce the influence of fuse and the rectification method.
3.3.1 Fuse Influence
Besides the previous short-circuit overcurrent performance, the fuse also has displacement effect, so under the condition of fuse displacement, overcurrent will occur because the circuit harness is not protected.
Under the condition of short circuit, when the fuse is disconnected, it means that it is the normal fuse position, and there is a short circuit phenomenon. However, the fuse does not change, indicating that it may burn out. However, if there is a short circuit phenomenon in B, it can play a protective role. If there is a short circuit phenomenon in A and B, the fuse will have a fusing effect, but the fusing time is long and the actual energy efficiency is insufficient, which will cause the burning problem.
3.3.2 Rectification Methods
Because there are many circuit harnesses in modern automobile products (which are consistent with the test conditions in this paper), the integrated protection means can't guarantee the actual energy efficiency. Therefore, in the rectification method, a fuse should be provided for each electrical equipment, and the independence of the fuse should be guaranteed. If any electrical equipment has a short circuit, the fuse can cut off the circuit in a very short time, and accordingly play a role in avoiding spontaneous combustion.
4. Conclusion.
This paper mainly analyzes the causes of auto-ignition of automotive circuit harness and its rectification. Through the analysis, it is concluded that there are three common causes of auto-ignition of automotive circuit harness, namely short circuit, closed circuit and abnormal fuse. Therefore, corresponding rectification methods should be put forward based on these problems. Around the content of the analysis, this paper has carried out relevant experimental work, and on the basis of the experiment, put forward relevant rectification methods, and introduced the functions of the methods.
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