Introducing multiple protection solutions for automotive wiring harness connections

Vehicle wiring plays an important role in the automobile, and the function and signal transmission of the automobile wiring are connected by the automobile wiring harness bridge, so the protection of the automobile wiring harness is also very important. Ordinary wiring harness will be protected by adhesive tape, and under special requirements or harsh environment, it will be protected by double heat-shrinkable tubes with high performance and strength. This paper introduces in detail the safeguard measures of vehicle wiring harness connection point, hole terminal and external wrapping protection measures, and discusses the selection of key maintenance waterproof sleeve and the use of wrapping raw materials, which provides data reference for developers. Vehicle wiring is an important part of the vehicle. The function of the automobile circuit and the transmission of the signal need the bridging connection of the automobile wiring harness. There are wiring harnesses in the whole vehicle, and the damage of the wiring harness directly affects the performance of the vehicle. There are several explanations in the QC/T29106-2004 standard about the conditions of low-voltage wiring harnesses for automobiles: automotive wiring harnesses should have high and low temperature, resistance to periodic changes in temperature and humidity, vibration resistance, smoke resistance and industrial solvent resistance. Therefore, it is very important to reinforce the outer protective layer of automobile wiring harness. Reasonable outer material and wrapping method of wiring harness can ensure the quality of wiring harness, reduce the cost and improve the economic benefit. This paper mainly introduces the external protection mode of automobile wiring harness and the selection and application of its materials.

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The 1、 protects the wire contact in the harness. The connection between the wires of the vehicle harness is called the harness node. It can be seen from the instrument harness, the body harness, the air conditioning harness and other harnesses that the harness contact can be used to realize the signal transmission and function realization between the switch and multiple electrical appliances. Therefore, the exposed contact needs to be protected. At present, in the field of automotive wiring harness, the contacts between multiple transmission and distribution lines are generally selected in three ways, namely, U-shaped terminal crimping, high-frequency welding and brazing. No matter which method is selected, the connected transmission wire core copper conductor will be exposed outside, if no protective measures are taken, the contact will be eroded by the environment and easily oxidized, and when multiple contacts are wrapped in the wiring harness at the same time, it is easy to cause the exposed copper wire between the contacts to pierce the skin of other conductors, resulting in short circuit of the automotive wiring harness. Serious cases may also cause car fires. Clauses 4.5.5 and 4.5.6 in QC/T29106-2004 of the conditions for automobile low-voltage wiring harness stipulate that the insulation layer on the surface of the harness in dry and wet areas must be excellent, the insulation layer material shall be closely attached to the contact part without deviation or falling off, and the insulation treatment position of the insulation layer at the joint point in the wet area shall be insulated by waterproof test, so that the insulation resistance is not less than 100MΩ. Therefore, the material with good insulation performance shall be selected to protect the wiring harness node. The harness connector adopts the most common U-shaped terminal crimping process at present, which is simple in operation, high in efficiency and stable in quality. Protective measures for the contact position of vehicle harness: ① Tape winding protection, including PVC tape and special cloth base tape. The width of the strip is about 40 mm, and the wrapping method is adopted. The wrapping is changed according to the size of the wiring harness connection point. Generally, the PVC tape is wrapped by 4 ~ 7 circles, and the cloth tape is wrapped by 2 ~ 4 circles. The binding method is mainly used for instrument harness, ceiling harness, vehicle body harness and other indoor harnesses, which are less affected by the environment. PVC tape is mainly used for control switches, signal transmission or wiring harness joints of small power circuits. However, the cloth tape is mostly used in the control of electrical circuits, with good temperature resistance, generally able to withstand 150 ℃ for a long time and 180 ℃ for a short time. ② Double-layer heat shrinkable tube heat shrinkable protection, according to the size of different harness contacts, there are quasi-4, quasi-5, quasi-6, quasi-9 and other specifications available. The length of the double heat-shrinkable tube varies with the length of the exposed copper wire and is generally 30 to 50 mm. Double heat shrink protection is usually used for the front compartment harness and the engine harness. This kind of application has a great impact on the environment, such as high engine temperature, bad weather and so on. The double heat-shrinkable tube can be completely sealed to achieve the effects of water resistance, high temperature resistance and wear resistance, and the natural cost is relatively high. 2. Hole-type terminal protection Hole-type terminal is generally used for grounding function. Usually, there is a grounding point on the body frame or engine shell. It is exposed to the outside air for a long time, especially in bad weather and environment. It is vulnerable to oxidation, resulting in increased connection resistance or open circuit. The terminal pressure wiring core should be well protected. Generally, single-layer or double-layer heat-shrinkable tubes can be selected. Single-layer heat-shrinkable tube can be selected for the internal harness, and double-layer heat-shrinkable tube can be used for the harnesses in the front compartment and the engine to protect the harnesses in the harsh environment. Generally, double-layer heat-shrinkable tube is selected for the grounding points such as the ABS. ECU on the vehicle to play a sealing role. In order not to be oxidized, some conductors that need to be exposed are also protected by heat-shrinkable tubes, such as heat-shrinkable tubes for shielding wires and shielding nets, which can be better protected.

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