Wire Harness design, how to choose wire type

The wire type of wire harness design mainly considers the environment and function of the wire harness.

The type of wire is also known as the type of wire. The first step in wire selection is to determine the type of wire. This section mainly introduces the type of automobile wire and the basis for wire type selection.

Classification of wires

Automotive harness commonly used wire types have Japanese standard (AVSS, etc.), national standard (QVR), German standard (FLRY), American standard and other major series. The appropriate type of wire can be selected according to the needs of users and different working environments.

1.Classification by standard

According to different standards, the low-voltage automobile wire is mainly divided into four series, such as national standard wire, Japanese standard wire, German standard wire and American standard wire. The choice of wire type mainly considers the environment and function of the wire harness, and there are many subcategories of wires under each standard series to choose from, such as:

1). National standard: QVR, QVR-105, QFR, QVVR, etc.

2). German standard: FLRY-A, FLRY-B, FLR4Y, FLR13Y, etc.

3). Day mark: AV, AVS, AVSS, CAVS, AVX, AEX, etc.

4). Us standard: GXL, TWP, TXL, GPT, HDT, STS, etc.

Characteristics of commonly used wires:

·The sun standard wire is characterized by thin insulation and good flexibility;

·National standard wire is characterized by thick insulation, relatively soft, good ductility;

·German standard wire insulation thinner, good flexibility;

·American standard wire insulation is generally thermoplastic or thermoset elastomer, and has been processed by irradiation process.

The appropriate type of wire can be selected according to the needs of users and different working environments. In the automotive industry, the German marking wire is currently used the most, and the Japanese marking wire is mainly used by Japanese cars.

The reference standards for different series of wires (reply the keyword "wire standard" in the public number of wire harness engineer to obtain all the following wire standards) are as follows:

1). National standard cable reference standard: GB /T8139, JB/T8139, QC/T730, QC/T1037

2). Japanese cable reference standards: JASO_D608, JASO_D609, JASO_D611, JISC_3406

3). German standard cable reference standards: ISO_6722, DIN_72550, DIN_72551, DIN_76772, VW_60306, LV_112-3

4). US standard cable reference standard: SAE_J1128, SAE_J1678, USAR-21.

2. Classification by use

From the point of use, the wire on the car harness can be roughly divided into ordinary wire, twisted pair wire and shielded wire.

1). Ordinary wire: used to transmit general power signals or relatively strong, not easily disturbed signals.

2). Twisted pair: used to transmit some weak signals or signals susceptible to interference, the role is to reduce the capacitance between the wires, the general bus and other digital signal circuits need to be twisted, generally 20-40 twisted per meter.

3). Shielding wire: used to transmit some weak signals or signals that are susceptible to interference, the system is used when the quality of the signal is particularly high, generally for analog signal circuits.

Ordinary wire is the most widely used, no more details.

Twisted pair wire is made of two ordinary thin wires with an insulating layer wrapped around each other in a certain proportion, as shown in the figure below:

Picture: Twisted pair

The terminal resistance of the CAN bus is 120Ω according to the characteristic impedance of the transmitted twisted pair. The characteristic impedance of twisted pair is related to its lay length. Transmission wire, does not allow wire diameter mutation, prevent characteristic impedance changes, cause reflection, resulting in signal distortion.

The twisted pair principle is that if the interference generated by the external electromagnetic signal on the two wires is equal and opposite, the interference signal will cancel each other. Twisted pair is the easiest way to eliminate interference, and twisted pair can be used in some cases where the requirements are not very strict.

Shielding wire is divided into aluminum foil shielding wire and braided mesh shielding wire, as shown in the following figure:

Figure: Shielded wire

Aluminum foil is mainly used to shield high-frequency electromagnetic waves to prevent high-frequency electromagnetic waves from contacting the conductor of the network cable to generate induced current and increase crosstalk. Braided net is generally braided by tin-plated round copper wire. Mainly to prevent low-frequency electromagnetic wave interference. Its working principle is the same as that of aluminum foil.

The working principle of the shielded wire: Taking the shielded wire of aluminum foil as an example, when the high-frequency electromagnetic wave comes into contact with the aluminum foil, according to Faraday's law of electromagnetic induction, the electromagnetic wave will converge to the surface of the aluminum foil and generate an induced current. At this time, a conductor is needed to introduce the induced current into the ground to avoid interference with the transmitted signal caused by the induced current. (Therefore, the shielding wire generally requires one end of the shielding layer to be attached to the iron and one end to be suspended.)

The black wire in the aluminum foil shielding wire is the wire, the braided net in the braided mesh shielding wire is the wire, and the aluminum foil shielding wire is generally used now, because the wiring harness processing operation is relatively simple.

Shielding is the most effective measure to avoid electromagnetic interference, because the external interference electromagnetic wave in the propagation process, encounter metal materials will not pass through, but is forced to change direction along the metal. Therefore, if the metal material is covered outside the equipment or wire to be shielded, and is connected to the earth through the ground wire, the interference electromagnetic wave will flow to the earth through the ground wire, and the signal in the shielded wire can be transmitted normally.

The following table shows the similarities and differences between twisted pair and shielded wire in five aspects: definition, cost, processing, function and application.

Comparison between twisted pair and shielded wire

2, the temperature resistance of the wire

According to the working environment temperature of the wire harness wire, choose different temperature resistance grade wires. The wire type of wire harness design mainly considers the environment and function of the wire harness.

Wire temperature rating is divided into 8 temperature grades (ISO6722), as shown in the following table:

Figure: ISO6722 definition of wire temperature resistance class

The external ambient temperature of the conductor

ⅰ. Cabin area: excluding engine, distance from engine exhaust pipe is more than 300mm, temperature range: Minimum=-40℃, continuous=100℃, Excursion=110℃

Ii, engine domain: located on the engine, distance from the exhaust pipe within 300mm, temperature range:

Minimum=-40℃, continuous=120℃, Excursion=130℃

Ⅲ, high temperature area: less than 150mm from the engine exhaust pipe, temperature range:

Minimum=-40℃, continuous=130℃, Excursion=150℃

ⅳ. Cockpit and chassis area: cockpit and chassis are more than 150mm from the exhaust pipe, temperature range:

Minimum=-40℃, continuous=80℃, Excursion=100℃

The wire traversing the above two areas should be selected with the temperature resistance grade meeting the temperature requirements of the two areas at the same time. The temperature resistance requirement of the region can be obtained from the temperature field, and then the type of wire selected can be determined from the temperature resistance grade of each wire.

1) According to the temperature resistance grade, according to JASO D611 standard, the daily standard wire is divided into:

① ordinary wire, temperature resistance 80℃, such as AV, AVS, AVSS, CAVS, etc.;

② Temperature resistant wire, temperature 100℃, such as AVX, AVSX, AVSSX, etc., temperature 120℃, such as AEX, AESSX, etc.

2) According to the temperature grade, according to the ISO 6722 standard, the German standard wire is divided into:

① temperature resistance 105℃, such as FLRY, FLR11Y, etc.;

② Temperature resistance 125℃, such as FLR9Y, FLR2X, FLR31Y, etc.

③ Temperature resistance 150℃, such as FLR13Y, FLR91X, FLR7Y, etc.;

④ Temperature resistance 180℃, such as FL2G, FLR7Y, etc.

According to the classification of the ISO conductor temperature Class, the current new models usually locate the conductor temperature Class B in the cockpit and cabin, and define the temperature class of the engine wire as Class C. For the conductor near the exhaust pipe area, the thermal insulation aluminum foil tape is usually used to protect the conductor to prevent the thermal radiation of the engine exhaust.