Quality control and improvement of vehicle engine wiring harnesses

In recent years, with the application of small displacement engines, the size of the engine is also shrinking, the space for wiring harness layout is getting smaller and smaller, but the requirements for the quality of wiring harness are getting higher and higher. Improving the quality of wiring harness has become an important task for automotive workers. 1. Brief introduction of engine harness The harness is the main nerve component of the engine and the power and signal transmission part of the sensor and actuator on the engine. The harness is an assembly composed of protective auxiliary materials such as connectors, terminals, wires and tapes, as well as electrical accessories such as fuses and relays. The quality of the harness in the engine is directly related to whether it and the ECU can work properly. 2. Faults and measures of engine harness When using engine harness, various engine problems will be caused by harness quality problems. This paper focuses on the control and improvement of a small displacement engine wiring harness in the process of research and development. 1. The operation is blocked and the engine is started or fails to change according to the set power and torque after starting. The main problems are: ① after the engine is powered on, the fuse is ablated; ② after the engine is started, the torque is limited to different degrees. The above problems are caused by the definition and manufacture of the harness design. Ablation of the engine electric fuse is due to the fact that the function definition of the ECU is completely inconsistent with that of the ignition coil, and the engine has torque limitation due to the fact that the power supply hole of the ignition coil is opposite to the signal hole of the camshaft position sensor. Therefore, the design and manufacturing shall be improved. The technical requirements are as follows: ① define the function definition of the actuator and sensor in the design to ensure that it is consistent with the function definition in the ECU; ② define the requirements according to the function definition of the drawing in the product manufacturing. After the improvement, the engine starts normally and can be changed according to the set power and torque. 2. When the harness is worn and the engine works normally and abnormally, read out the short circuit or fault of the engine sensor or actuator through INCA. After inspection, it is found that there are two situations: ① the engine harness is worn, resulting in short circuit or open circuit; ② the wire is ablated at the connector terminal connection, resulting in open circuit. Improve the design and production of wire harness: ① Due to the use of manual production, the wire harness size tolerance is relatively loose; Increase the clearance between the engine harness and the engine body by adding a tie on the harness to avoid the harness interference caused by the production tolerance. ② According to QC/T29106-2014 [1] Technical Conditions for Low-voltage Wiring Harnesses of Automobiles, the stability of the device is tested by adding a terminal drawing force test. 3. Signal instability The signal of the sensor or actuator is unstable during the experiment: ① The engine suddenly stalls; ② The signal of the camshaft position sensor is intermittent. Analysis: ① The copper wire in the power supply circuit wire of the ignition wire ring is disconnected, and the insulation layer is not cracked; ② The signal circuit terminal of the camshaft position sensor is not installed properly, and the terminal is out of position. The following measures shall be taken for the above problems: ① Standardize the crimping operation, and inspect the startup and replacement of the crimping die in accordance with QC/T29106-2004 Technical Conditions for Low-voltage Wiring Harnesses for Automobiles, and conduct spot checks in batches; ② Operators are required to operate in strict accordance with "one plug, two listen and three pull", and production line team leaders and quality inspectors shall conduct spot checks on finished products and semi-finished products. III. At the beginning of the quality management project of the wiring harness supplier, the supplier is explicitly required to provide a list of secondary suppliers of raw materials, conduct relevant performance tests on the raw materials, and finally conduct chemical inspection on the finished products. The corresponding test shall be carried out according to QC/T29106-2014 Technical Conditions for Automotive Low-voltage Wiring Harnesses and QC/T4132002 Basic Technical Conditions for Automotive Electrical Equipment [2]. The installation process of wiring harness shall be considered during design, and the reliability of wiring harness products shall be clearly specified according to the requirements of vehicle use environment and electrical performance. In terms of wiring harness performance, the first is to carry the engine for bench test verification, and the second is to carry out comprehensive durability test on the vehicle [3]. Wiring harness products shall also be tested for vibration resistance, salt spray, cold resistance, heat resistance, temperature change resistance and temperature and humidity cycle resistance. The performance of the vehicle line shall bear the comprehensive durability of the whole vehicle. The list of secondary suppliers of the wiring harness shall be determined. When the products are supplied in batches, it shall not be changed at will, and the process and product audits shall be carried out regularly for the suppliers. Clearly define the packaging of the harness product and ensure that the harness product is properly protected prior to supply. 4. Summarize that through the analysis of harness quality problems, the correction of problem points and the optimization of definitions, the faults of the gasoline engine harness have been significantly reduced by about 80%, and the relevant problems and corrective measures have been shared in lesson slearned, including the expansion of new products and ongoing products, so that similar quality problems will not recur.

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