Wire Harness is the neural system of the automobile circuit network, which connects the electronic components of the automobile and makes them function. With the continuous improvement of people's requirements for comfort, economy and safety, and the increasing variety of electronic products on automobiles, wire harnesses are becoming more and more complex. This requires improving the reliability, durability and other performance of the harness. The matching between various components of the harness is very important for vehicle safety. The selection of wire harness components should also be very careful and strict. This article will talk about the selection principle of automobile connector.
A Connector is mainly composed of Connector Housings, Terminals and Wire Seals.
1. Connector Housings: Used to fix and protect the terminal and ensure reliable locking after inserting.
2. Terminals: Transmitting current and electrical signal.
3. Wire Seals: For sealing and waterproofing.
2.1 Serialization——Terminals serialization, Housings serialization, Waterproof Seals serialization (Serialization with terminals as the core)
• Single terminal specification, universal mold in harness factory, improving production efficiency and crimping quality
• The housing structure is unified, which is convenient for the production and assembly of wire harness factory and vehicle factory
• Waterproof seals, Ring seals, and various accessories have unified specifications, improving the overall quality and performance
2.2 Assembly——Assembly Space, Touch Feeling, Sound, etc.
• Touchable: insertion force and touch feeling of terminal insertion housing
• Audible: When male housing is inserted into female housing, there is a clear sound
• Visible: When male housing is inserted into female housing, it should be a visual operation
• Assembly Space: according to the way of sheath assembly, there should be enough operation space
• Housing Size: suitable for hand operation
• Housing Structure: it can prevent terminal damage
2.3 Location & Environment——Select appropriate connector products according to Ambient Temperature, Sealing, Vibration, Chemical Reagents, etc.
• Ambient Temperature
√ Engine compartment: sealed, ambient temperature>105°C
√ Passenger compartment: unsealed, ambient temperature<85°C
• Sealing
√ Sealing type: single hole sealing & integral sealing
• Vibration
√ Installation position: Engine, Chassis, Engine compartment, Passenger compartment, etc
• Chemical Reagents
√ In the engine compartment and chassis, there are various liquids, such as Fuel, Brake Oil, Lubricants, Coolant, etc., as well as acidity and alkalinity in the external natural environment
2.4 Standards & Specifications——customer standards, domestic standards, international standards, performance test requirements
Generally, vehicle manufacturers have their own connector standards, which must be met when selecting. If not, the national standard QC/T417 can be implemented. The internationally accepted standards mainly include USCAR2.0
2.5 System requirements——entertainment system, safety system, power system
Generally, the whole system uses conventional connectors. However, there are some special requirements. For example:
• Air bag blaster requires a circuit breaker between terminals, and terminals require gold plating.
• The AV system may have special requirements for EMC.
2.6 Electrical factors——current, voltage drop, contact resistance, temperature rise
It is important for the connector to have a low resistance value throughout its life.
• Factors affecting resistance:
a. Volume resistance of material
b. Contact resistance of contact surface
• Danger of increased resistance:
a. The voltage drop at the connector may increase, resulting in abnormal operation of electrical appliances, and even loss of continuity.
b. With the increase of the contact resistance, the temperature of the contact also increases, which accelerates the increase of the resistance, eventually leading to the ablation of the connector, and even a fire in serious cases.
3.1 Selection of materials
• If the housing is inside the cab, the general ambient temperature will not exceed 85°C; If it is in the engine compartment, materials with good thermal stability should be selected according to the specific environmental temperature needs to ensure that the plastic has good stability at high temperatures.
• Common materials include PP, ABS, PA, PA66, PA6, PBT, etc.
• The housing can also add flame retardant or reinforcing materials in the plastic according to the actual situation to achieve the purpose of strengthening or flame retardant, such as adding glass fiber reinforcement, etc.
3.2 Structure selection——mainly select locking structure
The housing must have a locking structure, which can be easily installed and removed. When the locking is installed in place, you can obviously feel and hear the click sound. When the housing with primary locking and secondary locking to prevent the terminal from withdrawing is selected, it must ensure be locked
3.3 Selection of sealing——mainly select the sealing method and sealing grade
Corresponding waterproof methods shall be selected for the housings located in the wet area to prevent water, pollution and corrosion. The harsh environment includes the front compartment, wheel housing, chassis, doors, etc.
4.1 Selection of Series
Terminals are divided into Female terminal and Male terminal. Female terminal is the terminal matched by Female housing, also known as Socket terminal or Receptacle terminal. Male terminal refers to the terminal matched with Male housing, also known as Plug terminal or Tab terminal. The ‘Series’ we mentioned refers to the width of the Male terminal when the Female terminal matches the Male terminal, expressed in 'Tab width', and the unit is ‘mm’. For a company, the selected series should not be too many in terms of terminal selection. Generally, the 1.0, 2.8, 4.8, 6.3 and 9.5 series can meet the demand.
4.2 Selection of Structure
Mainly for the selection of female terminals：
• Large contact area
• Position limiting structure of spring tongue
• Multiple contact parts
• Try to select the terminal without hanging wing structure
4.3 Selection of Materials
• Brass
Brass, namely copper zinc alloy, is the most used terminal material with the lowest price, good conductivity, ductility and high plasticity. Due to the different zinc content in brass, the mechanical properties are also different, and the mechanical properties of brass vary with the zinc content. With the increase of zinc content from H63 to H59, they can withstand hot processing well, and are mostly used in various parts of machinery and electrical appliances, stamping parts and musical instruments.
• Phosphor bronze
Phosphor bronze is an alloy of copper, tin, and phosphorus. It is hard and has good elasticity, electrical conductivity and excellent machining performance，the insertion and removal are stable，so it is a frequently used material for terminals with spring tongue structure.
At the same time, it has strong fatigue resistance, high corrosion resistance and wear resistance under the condition of ensuring safety.
• Red copper
Red copper, which contains more than 99.9% copper, is generally called red copper because it has rose red color and is purple after forming oxide film on the surface. It has the highest conductivity, soft material, excellent thermal conductivity and plasticity. But the price is very high, so it is less used, generally used for R terminals, Y terminals or cable core.
4.4 Selection of Coating Material
Common electroplating types are Gold Plating, Silver Plating, Tin plating, Nickel Plating, etc.
● Gold
♦ The most ideal electroplating material
♦ Excellent corrosion resistance in any environment
♦ Excellent solderability
♦ Good ductility, easy to polish, high-temperature resistance, good resistance to discoloration
♦ Low contact resistance, good electrical conductivity
♦ Has certain wear resistance, also ensures the integrity of the signal
♦ Soft, must be reinforced with cobalt and nickel
♦ High cost
● Silver
♦ Excellent material for coating the surface of high current terminals, because it will not melt under high current
♦ Has a strong reflective ability and good thermal conductivity, electrical conductivity and welding performance
♦ Has strong chemical stability to organic acids and alkalis
♦ The cost is quite expensive, but cheaper than gold plating
♦ Easy to rust in the air with sulfur and chlorine
♦ Harder than tin, and its resistance coefficient is slightly higher than or equivalent to tin. Potential electron migration may lead to potential risks of connectors.
● Sn (Tin)
Tin is the most widely used coating material.
♦ Low cost
♦ Excellent electrical conductivity and solderability
♦ The tinned layer is soft and has good ductility (toughness) and corrosion resistance, which is conducive to a good fit between the plug and the socket
♦ The tin coating is bright silvery white for a better appearance
♦ Safe, non-toxic, and heavy metal free
♦ The tin layer is soft and easily damaged
♦ Lower corrosion resistance
● Nickel
♦ Anti-oxidation, and excellent corrosion resistance, nickel has strong passivation ability, can quickly form a very thin passivation film on the surface, and can resist the corrosion of atmosphere, alkali and some acids.
♦ The electroplated nickel layer has high hardness and high chemical stability in the air, which can improve the wear resistance of automotive electric terminals.
♦ The crystals are extremely fine, with excellent polishing performance, and can maintain their luster for a long time in the atmosphere.
♦ Reduces adverse reactions between host metal and coating metal
♦ Improve adhesion and solderability
Nickel can not only be used as a coating material but also widely used as the underlying material under the precious metal coating. The nickel-plated layer acts as a barrier layer between the copper layer and the gold layer, preventing the mutual penetration of gold and copper, blocking the substrate and the pores, thereby reducing the potential for pinhole corrosion; and providing a hard support layer beneath the precious metal plating, thereby increasing plating life and mechanical strength. The thicker the nickel base layer is, the lower the wear is. However, considering the cost and the roughness of the control surface, the thickness of 50-100u is generally selected.
4.5 Selection of Terminal Current Carrying
When passing the current, the terminal will generate heat. The relationship between its Temperature Rise and Current is shown in the figure. Even if the same terminal is used, its current carrying capacity is different due to different cable sizes.
With the increase of Ambient Temperature, the Current Carrying Capacity of the terminal will also decrease. At a certain Ambient Temperature, the terminal reaches thermal balance through a certain current, and the temperature no longer continues to rise. The current at this time is the Maximum Current that the terminal can withstand at this Ambient Temperature.
The graphs above show the temperature rise above ambient vs. current and the temperature derating curves for the 150 and 280 Series GT terminals using multiple cable sizes.
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Post time: Aug-03-2023