Basic knowledge of automobile connectors: analysis of automobile connector usage standards

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This article analyzes the use of automotive connectors and puts forward the importance of connector standards in the selection and application of automotive connectors. At the same time, from the three different connector standards QC/T-1067USCAR-2GMW-3191, the performance requirements of connectors from the use environment to the mechanical, electrical, and environmental durability of connectors are analyzed in detail. With the rapid development of China's automobile industry, automobiles have expanded from satisfying the initial transportation function to now having a lot of safety and comfort functions. With the increase in functions, automotive connectors, as key components of automobiles, have developed from dozens of connectors used in one car to hundreds of connectors used in one car today, with more than one hundred varieties; from the previous 6.3 specifications to the current 0.64 specifications. And these more than one hundred connectors are distributed in the cab, body, door, engine compartment, transmission and other places. Because the use temperature and vibration level of connectors in different places are different, the requirements for the protection level of connectors are different, so different use environments have different performance requirements for connectors.


1 Analysis of the usage status of automotive connectors

Taking two foreign and domestic car models as examples, the connector usage specifications and manufacturer distribution are analyzed.

1) The proportion of connector specifications for a certain foreign brand of automobile is shown in Figure 1.

This model has a total of 205 connectors, of which 90 are 0.64-size connectors, accounting for 43.9% of the total number of connectors developed; 25 are 1.2-size connectors, accounting for 12.2% of the total number of connectors developed; 30 are 1.5-size connectors, accounting for 14.63%; 20 are 2.8-size connectors, accounting for 9.76%, etc. These connectors are from different brands, including TE, THB, Molex, JAE, YAZAKI, APTIV, Bosch, SUM, etc.

Figure 1 List of connector specifications for a certain foreign vehicle model

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2) The proportion of connector manufacturers in a domestic joint venture brand car is shown in Figure 2.

Figure 2 List of connector specifications for a certain domestic vehicle model

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This model has a total of 265 connectors, of which 93 were 0.64, accounting for 35.09% of the total; 12 were 1.2, accounting for 4.53% of the total; 41 were 1.5, accounting for 15.47%; 23 were 1.8, accounting for 8.68%; 33 were 2.2, accounting for 12.45%; 16 were 2.8, accounting for 6.04%, etc. These connectors come from manufacturers such as TE, THB, SWS, Molex, KET, APTIV, and YAZAKI.

3) From the above data, we can judge that there are more than 10 connector suppliers used in domestic and foreign models, and the specifications used range from 0.5 specifications, 0.64 specifications to 9.5 specifications, etc. More than 8 specifications. From the data analysis, when selecting and developing connectors for new models, the OEMs not only need to consider the specifications, usage locations, and protection level requirements of the selected connectors, but also need to select a connector that best suits the model and function from different products of different manufacturers. This requires a standard to support and guide the corresponding engineers of the connector manufacturers to select the most cost-effective and most suitable functional connector.


2 Analysis of automotive connector usage standards

2.1 Current Distribution of Automotive Connector Standards

There are many connector standards at present, from the earlier international standard ISO 8092, SAE standard USCAR-2, to the latest revised industry standard QC/T-1067-2017 (replacing QC/T-417) in China. At the same time, many automobile companies have also defined their own connector standards, such as Volkswagen's VW 75174, GM's GMW-3191, SAIC's SMTC 3 862 001, Geely's Q/JLY J7110195C, etc. Because there are so many standards, and there are many similarities and differences between different standards, this article focuses on the three most widely used standards in the world, namely USCAR-2-6, QC/T-1067-2017, and GMW 3191-2012.

2.2 Definition of connector use environment in connector standards

For a connector, the ambient temperature, current carrying capacity, protection level, vibration resistance and other specifications of the connector will be defined in its specification sheet at the beginning of research and development. Connector selection engineers need to understand the different requirements of connectors in different use environments, which is also defined in detail in the current use standards. The standard definition of QC/T-1067 is shown in Table 1 to Table 3, the standard definition of GMW-3191 is shown in Table 4 to Table 6, and the standard definition of USCAR-2 is shown in Table 7 to Table 9.

Table 1 QC/T-1067 temperature grades

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Table 2 QC/T-1067 vibration levels

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Note: The elastic part refers to the part on the vehicle body that is supported by the suspension system. The elastic part does not include tires, wheels, brake discs (drums), etc.

Table 3 QC/T-1067 sealing grade

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Table 4 GMW-3191 Temperature Class

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Table 5 GMW-3191 Vibration Class

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Table 6 GMW-3191 Sealing Class

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Table 7 USCAR-2 Temperature Classification

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Table 8 USCAR-2 Vibration Classification

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Table 9 USCAR-2 Sealing Classification

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From the definitions of the above standards, it is clear that the current definitions of the three major standards for connector protection levels are consistent according to different usage locations, and they define the S1 unsealed area, S2 sealed area, and S3 high-pressure water jet area respectively.


In the definition of temperature grade, we found that the three major standards divide the operating temperature into five levels according to the different use positions of the connector; at the same time, QC/T-1067 and USCAR-2 both clearly state that the temperature grade of -40~85℃ is not recommended, but this temperature grade is recommended in GMW-3191 for connectors installed in the cab as the experimental ambient temperature.


In the definition of vibration levels, by comparing the detailed vibration frequency and power spectral density (PSD) of the standards, it is known that the vibration levels V3, V4, and V5 defined in QC/T-1067 and USCAR-2 correspond to and are equivalent to levels 2/4/3 in GMW-3191 respectively.


At the same time, GMW-3191 defines the vibration level and applicable parameters of the transmission connector, which are not defined in USCAR-2 and QC/T-1067. However, USCAR-2 and QC/T-1067 define the vibration level and applicable parameters of the connector installed on the engine but not on the parts with severe vibration, which are not defined in GMW3191. See Tables 10 and 11.


Table 10 Summary of information on the same vibration level of QC/T-1067, USCAR-2, and GMW-3191

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Regarding vibration tests, we mainly verify whether the performance of the connector system meets the requirements under simulated actual vehicle vibration conditions. Because under vibration or vibration impact conditions, it will cause plating wear on the terminal contact surface, positive pressure attenuation, and mechanical failure of supporting plastic materials. Therefore, it is necessary to continuously monitor the contact resistance in the vibration test and ensure that the contact resistance in the circuit exceeds 7Ω (or 1Ω) for no more than 1 microsecond.


Through the definition and analysis of the connector usage environment in the above different standards, we understand that when selecting a connector for a certain function, we must first understand the location where the function is used, and then determine the temperature level, vibration level, and protection level that the connector needs to withstand based on the location of use, and make the best selection.


2.3 Definition of connector mechanical properties in connector standards

Currently, USCAR-2 defines 18 items of connector mechanical properties, QC/T-1067 defines 20 items of connector mechanical properties, and GMW-3191 defines 21 items of connector mechanical properties, as shown in Table 12, Table 13, and Table 14 respectively.


By comparing the mechanical properties of the three standards, we understand that the mechanical properties in the current connector standards are mainly concentrated in the following points: the bending strength of the terminal itself; the plug-in and pull-out force between the terminal; the insertion force, retention force, thrust force, and polarization test between the terminal and the connector; the insertion force, separation force, unlocking force, and polarization test between the connector and the connector; the assembly force and retention force of the connector terminal secondary lock (TPA); the assembly force and retention force of the connector secondary locking structure (CPA); the mechanical strength of the connector assisting structure; the mechanical strength of the connector fixing structure; the retention force of the sealing ring; and the retention force of the board end pin.


Table 11 Summary of different vibration level information of QC/T-1067, USCAR-2 and GMW-3191

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Note: NA means not defined in the corresponding standard.

Table 12 20 mechanical properties test items of QC/T-1067 standard

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In addition to the above, GMW-3191 also requires the crimping performance of the terminal, which is a very important performance test that directly affects the contact resistance of the entire terminal (the crimping resistance is included in the contact resistance). Although there is no requirement in USCAR-2 and QC/T-1067, this test has very detailed requirements in USCAR-21, so experienced engineers will collect the corresponding crimping reports when selecting connector terminals.

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Reference address:Basic knowledge of automobile connectors: analysis of automobile connector usage standards

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