How to choose automotive wiring harness and connector?

With the increasing popularity of automobiles, the problem of how to choose the wiring harness and connectors has become the doubt of many automakers and buyers.Konnra Electronics is here to help you choose the wiring harness and connectors for your car.

Automotive low voltage wire
The 600V withstand voltage is a low-voltage electric wire in the electrical classification, and it has become a low-voltage electric wire for automobiles because it is attached to the characteristics of a car in the automobile field. The wires are also classified into a heat resistant type and a thin type depending on the material thickness of the insulator.
A) Construction of the conductor

B) Insulator

In order to prevent the burning of electric wires due to heat generation, a flame retardant is added in advance in the insulator. The flame retardant is also a plastic material, which acts to soften the insulator. At high temperatures, the flame retardant will be released and the insulator will harden. As the car vibrates, cracks appear and the wires are exposed. If you continue driving under such conditions, it is likely to be one of the causes of electrical shorts.
Shielded wires and strands for automobiles:
In recent years, in order to develop high-performance/comfortable, the automotive industry is gradually converting from a switch-control function to an electronic device that automatically senses driving/environmental changes and selects the most suitable state for driving.
To perform such complicated control, what is needed is a precision electronic instrument that can calculate a lot of information in an instant without error. In addition, the sensor is required to sense driving/environmental information by a weak current change, and ON-OFF can be switched rapidly (digital signal) when the current changes.
In this case, if a high-current electric wire is placed together with a high-voltage electric wire (ignition system, electric wave), a high voltage will damage a semiconductor component in a precision electronic instrument, and a sensor circuit affected by the electric wire will flow and be turned ON. The same current as the -OFF signal causes an operation error.
Therefore, in order to avoid the influence of large current and high voltage externality, shielded wires and stranded wires are used on important digital loop wires.
A) Shielded wire

Type and characteristics

We use a shielded metal wire that is wrapped around the wire to reflect electromagnetic waves from the outside as a shielded wire.
The following are the types and characteristics of shielded wires:

NameShielding materialCharacteristicTransverse bandaging shieldTin-coated soft copper wire or soft copper wire (0.12sq)In the frequency range of (10MHZ), compared with mesh multi-core shielding performance is low, but the outside diameter is fine, processing performance is superior.Mesh screenTin-coated soft copper wire or soft copper wire (0.12sq)Its shielding performance is also superior at high and low frequencies.Foil (Copper) shieldingCopper foilShielding function and mesh shielding line, but shielding line because of simple processing, so superior processing performance.Foil (Aluminum) shieldingAluminum foilShielding function is the lowest, but with good processing, light weight characteristics.

B) Stranded wire
Effect of stranded wire
We refer to a wire that twists two wires together as a stranded wire or a 2-core wire, which is a method for effectively preventing electromagnetic wave interference. As shown in Fig. 2, the electromagnetic waves generated by the current lines can be cancelled according to the inversion of each ring.

Figure 1 shows the direction of the current generated by the strands under the induction of electromagnetic current.

Figure 2 Cancellation effect of twisted wires

If the current line through which the electromagnetic current flows is parallel to the signal line, the induced current in the same direction will be generated regardless of which line. However, if the power supply line through which the electromagnetic current flows is the same as the twisted line of the signal line, the induced current generated by the signal line is opposite to the direction.

The car wiring harness is the main body of the car circuit, and there is no car circuit without the wire harness. As people’s safety, comfort, economy and emissions requirements increase, the wiring harness of the car becomes more and more complicated, but the space for the wire harness is getting smaller and smaller. Therefore, how to improve the overall performance design of automotive wiring harness has become the focus of attention, and automotive wire harness manufacturers no longer simply engage in wire harness design and manufacturing, and the pre-development of automobile host manufacturers has become an inevitable trend. Based on years of experience in wire harness design and manufacturing, Konnra Electronics talks about the general design process and design principles of wire harnesses.

(I) the vehicle circuit design

(1) Power distribution design
Whether the design of the power supply system of the car is reasonable is directly related to the normal operation of the car electric device and the safety of the whole car. Therefore, the starting point of the car wiring harness design in all countries in the world is basically based on safety. The vehicle electrical system consists essentially of three parts.
Battery direct power supply system (generally called normal power or 30 power). The load connected to this part of the power supply is generally a safety component or an important part of the car. The main purpose is to control as little as possible when supplying power to these parts, to ensure that these parts can work normally even if the car does not start up. Go to the site for maintenance, etc. Such as: engine ECU and engine sensor operating power, fuel pump operating power, ABS controller power, diagnostic interface power supply.
Ignition switch controlled power supply system (generally referred to as IG file or smart). This part of the electrical device is basically used only when the engine is running, and the power supply from the generator avoids the possibility of competing for power when charging the battery. Such as: instrument power supply, brake light power supply, airbag power supply, etc.
The power supply of the load (generally referred to as the ACC power supply) is removed when the engine is started. This part of the electrical device generally has a large load and does not have to work when the car is started. Generally a little cigarette lighter power supply, air conditioning power supply, radio and power supply, wiper power supply, etc.
(2) Line protection design
Line protection is to protect the wires and protect the loop electrical components. The protection device mainly has a fuse, a circuit breaker and a fusible link.
a. The principle of selection of fuses
Engine ECU, ABS, etc. have a great impact on the performance and safety of the whole vehicle. In addition, electrical components that are susceptible to interference from other electrical equipment must have a single fuse.
Engine sensors, various types of alarm lights, external lighting, and other electrical components have a greater impact on vehicle performance and safety, but such electrical loads are not sensitive to mutual interference. Therefore, such electrical loads can be combined with each other depending on the situation, and a fuse can be used in common.
The electric load of the general electric device type provided for the purpose of increasing the comfort can be combined with each other according to the situation, and a fuse is used in common.
The fuses are divided into fast-melting and slow-melting. The main component of the fast-acting fuse is a thin tin wire. The chip fuse is widely used because of its simple structure, reliability, vibration resistance and easy detection. The slow-melt fuse is actually a tin alloy piece. The fuses are typically connected in series to an inductive load circuit, such as a motor circuit.
Resistive and inductive loads should avoid using the same fuse as much as possible.
Generally calculate and determine the fuse capacity according to the maximum continuous operating current of the electrical device, according to the empirical formula: fuse rated capacity = maximum operating current of the circuit ÷ 80% (or 70%).
b. Breaker
The biggest feature of circuit breakers is recoverability, but it is costly and less used. Circuit breakers are generally thermo-mechanical devices that utilize different thermal deformations of the two metals to open or close the contacts or self-switch. The new circuit breaker uses PTC solid material as an overcurrent protection component, which is a positive temperature coefficient resistor that is turned off or on depending on the current or temperature. The biggest advantage of this protection element is that it can be switched on automatically after troubleshooting, without manual adjustment and replacement.
c. Fusible line
The characteristic of the fusible link is that when the line passes a huge overload current, the fusible link can be blown for a certain period of time (generally ≤ 5 s), thereby cutting off the power supply and preventing a malignant accident. The fusible link is also composed of a conductor and an insulating layer. The insulating layer is generally a chlorosulfonated polyethylene material, because the insulating layer is thick, so it is seen. It is thicker than the wire of the same specification.
The fusible link is usually connected to the circuit directly led out by the battery. Commonly used cross-sections of fusible links are 0.3mm2, 0.5mm2, 0.75mm2, 1.0mm2, 1.5mm2, and even larger cross-section fusible wires such as 8mm2. The length of the wire segment of the fusible link is divided into three types: (50±5) mm, (100±10) mm, and (150±15) mm.
The fusible link should have an obvious mark. When it is blown, its mark should still exist for easy replacement. The melting characteristics of the fusible link are shown in Table 1.
Table 1 Fuse characteristics of fusible wire
ItemsDetailsThe specification of fusible wire/mm20.30.50.7511.5Mark(Insulation color)PurpleBrownRedBlueYellowFusing current(empirical value)/A150200250300350Melting time≤5

(3) Selection and design of relays

The relay is divided into two types, current type and voltage type. Generally, whether or not to use a relay is determined according to the power of the electric appliance and the bearing capacity of the switch. Commonly used relay devices generally include wipers, horns, defrosting, headlights, fog lamps, fans, blowers, turn signals (flashers), and the like. The relays are divided into 6V, 12V, and 24V. The commonly used relays are rated at 12V.
Technical requirements for the selection of relays: 1 good reliability; 2 stable performance; 3 light weight, small size, long life, small impact on surrounding components; 4 simple structure, good processability, low cost.
(4) Design rules for ground distribution
Engine ECU, ABS, etc. have a great impact on the performance and safety of the whole vehicle, and are easily interfered by other electrical equipment, so the grounding points of these parts must be set separately.
For the airbag system, its grounding point should not only be single, but also to ensure its safety and reliability, it is best to use double grounding. The purpose is that one of the grounding rails fails, and the system can ground the iron through another grounding point to ensure the safe operation of the system.
In order to avoid interference, the radio system must also be grounded separately.
The grounding of the weak signal sensor is preferably independent, and the grounding point is preferably closer to the sensor to ensure the true transmission of the signal.
Other electrical devices can share a common ground point with each other according to specific arrangements. The principle is to tie the iron near, to avoid the excessive length of the wire, causing unnecessary voltage drop.
The battery negative line, engine ground wire, etc. due to the large cross-section of the wire, it is necessary to control the line length and direction, reduce the voltage drop; in order to increase safety, the engine, the body is generally connected to the negative pole of the battery;
Grounding method: First, the iron is passed through the hole joint. This method must be insulated with heat-shrinkable tube at the tail of the joint; the second is to directly lap the iron through the inner short-circuited sheath.
(II), the three-dimensional layout of the harness is designed
This process is mainly to simulate the harness direction and diameter of different areas, consider the sealing and protection of the wiring harness, and simulate the fixing position and fixing mode of the wiring harness, as shown in Figure 1. The main software for 3D wiring is PRO-E, UG and CATIA.
Third, the selection design of the connector
The connector is the core component of the harness, and the performance of the connector directly determines the overall performance of the harness, and plays a decisive role in the stability and safety of the entire vehicle.
(1) Selection principle of selection of connectors
The connector is selected to ensure good contact with the electrical device, the contact resistance is minimized, and the reliability is improved. The connector of the double spring type compression structure is preferred.
The connector is reasonably selected according to the cross-sectional area of the wire and the magnitude of the passing current.
The jacket in the engine compartment is connected to the jacket. Because the temperature and humidity in the cabin are too large and there are many corrosive gases and liquids, it is necessary to choose a waterproof jacket.
If the same sheath is used in the same harness, the color must be different.
Based on the overall coordination of the exterior of the car, a black or dark jacket should be preferred in the engine compartment.
In order to reduce the type and number of sheathing butt joints, it is preferred to use a hybrid type to make the assembly convenient.
For terminal connectors for airbags, ABS, ECUs, etc., which require high performance, gold-plated parts should be preferred to ensure safety and reliability.
The battery connector (battery clip) has a cone inside and a taper of 1:9; the battery clip is made of tin-plated copper, galvanized copper or lead-bismuth alloy.
The currents that can be carried by plugs of different specifications are generally as follows: 1 series, about 10A; 2.2 or 3 series, about 20A; 4.8 series, about 30A; 6.3 series, about 45A; 7.8 or 9.5 series, about 60A.
(II) Performance analysis of raw materials (materials) of connectors
1. Sheath material (plastic parts)
Commonly used materials are mainly PA6, PA66, ABS, PBT, pp, etc., I have summarized their specific performance differences. When designing the plug-in, different materials can be selected according to different needs. Flame-retardant or reinforcing materials can be added to the plastic according to the actual situation to achieve the purpose of strengthening or flame retardant, such as adding glass fiber reinforcement.
2. Terminal material (copper)
The copper used for the connectors is mainly brass and bronze (the hardness of brass is slightly lower than that of bronze), and brass accounts for a large proportion. In addition, different coatings can be selected according to different needs.
Four-wire selection design
(1) Choice of wire type
The wire harness design uses the wire type to focus on the environment and function of the wire harness. For example, the ambient temperature around the engine is high, and there are many corrosive gases and liquids. Therefore, it is necessary to use high temperature, oil, vibration and friction resistant wires; the wires on the trunk lid should maintain its elasticity at low temperatures, so use cold elastic wires to ensure normal operation; the wires on the automatic transmission must be resistant. High temperature and hydraulic oil resistance have good temperature stability; weak signal sensors use shielded wires, such as knock sensor and crank position sensor, ABS wheel speed sensor, etc.; the inner wire has high bending resistance requirements.
Commonly used wires for automotive wiring harnesses usually use stranded copper wires, and the insulation is PVC insulation. The wire harness wire should have the characteristics of temperature resistance, oil resistance, wear resistance, water resistance, corrosion resistance, oxidation resistance and flame retardancy.
The types of wires commonly used in automotive wiring harnesses include Japanese standard (AVSS, etc.), national standard (QVR), German standard (FLRY), and American standard. AVSS (AVS) wire is characterized by thin skin insulation and good flexibility; QVR is characterized by thick insulation, soft and good ductility; German standard wire insulation is thinner and flexible; American standard wire insulation is generally Thermoplastic or thermoset elastomers, as well as processed by irradiation. The appropriate type of wire can be selected according to the needs of the user and different working environments.
(2) Calculating the cross-sectional area of the selected conductor
Calculate the current of the circulating wire according to the power of the electrical device; the electrical equipment that works for a long time can select the wire with the actual current carrying capacity of 60%; for the short-time working electrical equipment, the wire with the actual current carrying capacity of 60%-100% can be selected.
The cross-sectional area of the wire is appropriately changed according to different working environments and temperature.
The cross-sectional area of the wire is appropriately changed according to the direction of the wire and the number of connectors (ie, the magnitude of the voltage drop).
Regarding the calculation of the cross-sectional area of the wire, some experts have concluded some empirical formulas: I=P/UsA=IρL/Ud
Where: I — current; P — power; Us — system voltage; A — wire cross-sectional area; Ud — allow maximum voltage drop loss; ρ — copper resistivity; L — wire length.
Or according to the following empirical formula: I=A×10+8/2
The empirical theoretical value of the allowable current flow and the cross-sectional area of the conductor (more than the calculated value according to the above formula)
Five, the design of the whole vehicle wiring harness seal (rubber parts)
When the automobile wiring harness is through the hole, the rubber member is generally used for the transition to play the functions of wear resistance, waterproofing and sealing. Mainly distributed in the following parts: the interface between the engine and the cab, the interface between the front compartment and the cab (two places on the left and right), the four-door (or back door) and the compartment interface, the inlet of the fuel tank.
Commonly used materials are generally natural rubber, neoprene, silicone rubber, EPDM, and the like.
Characteristics of natural rubber: good elasticity and mechanical strength, excellent flexural resistance, high tear strength and good cold resistance. Disadvantages: The aging resistance is not good, it is not resistant to oil and ozone, and it is flammable.
The characteristics of neoprene: good resistance to ozone, heat aging, oil resistance, flame retardancy and self-extinguishing; but low temperature resistance.
Characteristics of silicone rubber: heat resistance, cold resistance and weather resistance are good; the disadvantage is that it is not resistant to oil. The characteristics of EPDM: weather resistance, ozone resistance, heat resistance, corrosion resistance, acid and alkali resistance, etc., and high strength and high expansion ratio; Disadvantages: poor adhesion, and no natural elasticity Good rubber and poor oil resistance.
In comparison, the comprehensive performance of EPDM is better, so the rubber parts for automotive wiring harnesses are generally selected from EPDM materials.
Sixth, the entire vehicle wiring harness and fixed design
(I) Harness wrapping design
The wire bundle is wrapped out to wear, flame retardant, anti-corrosion, prevent interference, reduce noise, and beautify the appearance. Generally, the following dressing design scheme is formulated according to the working environment and space.
The engine harness has a harsh working environment, so it is completely wrapped with a bellows with high flame retardancy, water resistance and high mechanical strength.
The working environment of the front cabin is also relatively poor. Most of the branches are also wrapped with a flame-retardant bellows, and some branches are wrapped with PVC pipes.
The instrument line has a small working space and a relatively good environment. It can be wrapped or wrapped with tape.
The door line and the ceiling line have a small working space, which can be completely wrapped with tape, and some branches can be wrapped with industrial plastic cloth; the thin top line can be directly glued to the body with a sponge tape.
Since the chassis wire has a large number of contact parts with the vehicle body, it is wrapped with a bellows to prevent wire harness wear.
(II) Performance analysis of raw materials for dressing
1. Bellows
Bellows generally account for about 60% or more in wire bundle dressing. The main feature is that the wear resistance is good, and the high temperature resistance, flame retardancy and heat resistance are good in the high temperature zone. The temperature of the bellows is between -40 and 150 °C. Its material is generally divided into PP and PA2. PA material is superior to PP material in flame retardant and wear resistance; however, PP material is stronger than PA material in bending fatigue resistance.
2. PVC pipe
The function of the PVC pipe is similar to that of the bellows. The PVC pipe has good flexibility and bending resistance, and the PVC pipe is generally closed, so the PVC pipe is mainly used for the branch of the wire harness to make the wire smoothly transition. The heat resistance temperature of the PVC pipe is not high, generally below 80 °C.
3. tape
The tape acts as a bundle, wear, insulation, flame retardant, noise reduction, marking, etc. in the wire bundle, and generally accounts for about 30% in the wrapping material. The wiring harness tape is generally divided into three types: PVC tape, air-laid cloth tape and cloth tape. PVC tape has good wear resistance and flame retardancy; the temperature resistance is around 80 °C, the noise reduction is not good, and the price is relatively cheap. The flannel tape and the cloth tape material are PET. The banding property and the noise reduction of the flannel tape are the best, and the temperature resistance is about 105 °C; the abrasion resistance of the cloth tape is the best, and the temperature resistance is up to 150 °C. The common disadvantage of flannel tape and cloth tape is that it is not flame retardant and expensive.
(III) Harness fixed design
The central electrical box is generally fixed by steel bars, bolts, etc., or directly mounted on the vehicle body by a fixed structure designed by the electrical box itself.
Each wire harness is generally fixed in the body hole with a plastic cable tie, a hook, or the like. Most of the body holes are round holes or elliptical holes, and the diameters are generally 5mm, 6mm, and 7mm.
The sheaths that are butted between the bundles are generally collectively fixed by a sheath bracket and mounted on the vehicle body.