Automotive wiring harness design ideas and parts selection

Automotive wiring harness design ideas and parts selection

Abstract: The automobile wiring harness is an important part of the automobile circuit. The reasonable design of the automobile wiring harness is one of the conditions for ensuring safe driving of the car. This article introduces the design process of automobile wiring harness and the selection of core raw materials. Principle design and 3D layout are essential aspects of wire harness design. The correct selection of key raw materials such as connectors, wires, and protective materials is the basis for the automotive wiring harness to function as it should.

Introduction

The basic idea of automobile wiring harness design is to determine the circuit loops according to the needs of the electrical equipment and calculate the voltage and current of each loop, especially the high-power equipment, select the matching connector according to the electrical equipment, determine the cross-sectional area of the wire harness according to the current, and then design Wire harness direction.

Wiring Harness Design Overview

1 The basic process of wire harness development and design is as follows:

(1) According to the function table required by the OEM, list all functional parts connected to the wiring harness, confirm the component functions with the corresponding electrical engineer, obtain ICD information, and determine the electrical schematic layout. Check the principles of each ECU system and integrate each functional component into a completed wiring harness schematic diagram. Generally, the power supply system and grounding parts can be merged together using riveting points. At the same time, check the current size of each functional system (including overcurrent or stalled current, etc.) to ensure that it can meet the working needs of electrical systems such as motors, switches, fuses, hair dryers, etc.

(2) Design a preliminary 3D distribution diagram, and use CATIA or UG software to complete the distribution of the wire harness according to the processing and assembly sequence of the general wire harness process. During this process, the installation location of the fuse box must be basically defined, and a certain margin must be reserved in the initial 3D distribution drawing.

(3) Convert 2D drawings. 2D drawings refer to industry standards. For example, the QC29106 standard has relevant requirements.

(4) According to the initial 2D drawings, make hand-made wiring harness samples and test-install them in the car.

(5) Based on the actual trial installation results and trial operation results, the wire harness 3D wiring engineer optimizes and adjusts the wire direction or length, taking dynamic conditions into consideration.

(6) The wiring harness is installed and connected to the electrical functional parts of the vehicle. Due to the installation requirements of each electrical system or the vehicle, the wiring harness generally needs to be continuously adjusted and optimized in conjunction with each system. That is, the entire development process is also designed to be continuously optimized and updated. process.

Design method

Principle design of wiring harness

(1) Ask the OEM for vehicle electrical functions, current requirements and other special requirements. And confirm all information such as the installation location of electrical components, the assembly method of electrical components and wiring harnesses, and the working environment.

(2) Make electrical schematic diagrams and circuit layout drawings with reference to the functions and methods that customers need to implement.

(3) Distribute energy to each electrical component system, including distribution of power cords and grounding wires.

(4) Determination of wire diameter. First, the current that needs to pass through the wire is obtained from the actual power of the electrical device; long-term working components use wires with 60% of the actual current carrying capacity (such as heating systems, entertainment systems, security systems); short-term working components use 60%-100% of the actual current carrying capacity wires between. (such as seat adjustment motor, window lift motor, angle adjuster, etc.).

3D wiring design

The three-dimensional direction of the wiring harness is generally based on the premise of satisfying the electrical installation of the entire vehicle, combined with the body sheet metal layout direction and opening and slotting design, to carry out the overall layout. In particular, the segmented design and trunk positioning of the wiring harness must consider the overall layout.

2.1 Requirements for three-dimensional wiring of automobile wiring harnesses

The three-dimensional wiring of automobile wiring harness is a complex project from beginning to end. The main points are as follows:

(1) Ensure that all electrical functional areas are easy to assemble, and the final assembly section is as simple as possible to facilitate installation. If there are parts that are not suitable for direct installation, you can consider built-in counterpart parts, which can be installed separately and then assembled together (this will increase the cost). Door panels, interior trim and other tail lines can be assembled separately. The assembly process can be realized by ensuring the traditional process and tooling as much as possible.

(2) In addition to assembly, attention should also be paid to maintenance and repair. It also needs to be easy to disassemble, which is commonly known as DFD (design for disassembly). During maintenance, only a section of the wire is removed, which is much easier to operate than removing the entire wire harness and saves money at the same time. costs and reduce hidden risks.

2.2 Other details of wiring harness layout

In addition to the convenience of assembly and disassembly mentioned above, the wiring harness layout also needs to consider the following details:

(1) Reserve enough margin, (even under the lower limit of tolerance), especially for wire harnesses between two or more components with relative motion, the length required at the extreme position must be considered.

(2) The wire harness cannot be kept in a tight state, otherwise it will continue to form internal stress on the copper wire and accelerate its aging process.

(3) Wiring harnesses generally need to be fixed with buckles or slots at intervals, and cannot be too long and free.

Part selection

Wire selection

When selecting wires for a wire harness, focus on the functions and environment that the wire harness needs to achieve. For example, for engine wiring harnesses, the temperature inside the cabin is very high and there are many corrosive substances, so materials that are high temperature and resistant to oil corrosion should be selected, such as Teflon or cross-linked PE.

The trunk or door undergoes frequent repeated movements, so choose a wire harness with relatively high elasticity, such as TPE or rubber. For some weak signal types, composite shielded wires are generally used, such as knock sensor wire harnesses, etc. The requirements in the cab are relatively low, so you can consider using PVC wire harnesses, which can save costs and be beneficial to lightweighting.

Connector

The connector is the most important component of the wiring harness. It directly determines whether the wiring harness can achieve the core connection function and plays a decisive role in the stability of the electrical system.

2.1 Selection requirements for connectors

The first is the cooperation with electrical components. The mechanical insertion retention force meets the usage requirements. The design with secondary lock is preferred. Contact resistance is as low as possible. Insulation resistance and overcurrent meet the operating current requirements of the conductor. For wire harnesses in wet areas, it is necessary to choose a waterproof sheath and match it with a suitable sealing ring or blind plug to meet the requirements of different waterproof levels in different areas.

2.2 Performance of connector raw materials

①Sheath material (plastic parts):

At present, the commonly used materials for connectors mainly include PA66, PBT, ABS, etc. It is generally necessary to add some additives to increase the performance of the material, such as adding glass fiber to increase strength and adding plasticizer to increase softness.

②Terminal material (copper):

The commonly used materials for terminals are brass, bronze and copper alloys. Brass has strong wear resistance, bronze has good castability, wear resistance and stable chemical properties. Copper alloy has excellent electrical conductivity, thermal conductivity, ductility and Corrosion resistance. In addition, considering salt spray and aging, terminals generally need to be added with different plating layers, such as tin plating, gold plating, etc.

2.3 Connector classification

According to the connector matching form, it can be divided into: wire-to-wire and wire-to-board.

① Line to line

Wire-to-wire connections include wire-to-cable or cable-to-cable forms, and their defining characteristic is that two single-wire individuals or corresponding conductors in two cables are permanently connected to each other.

②Wire to board

The wire-to-board connection is mainly a connection in which one end of the connector is connected to a wire or cable, and the terminals on the other end of the connector are fixed and connected to the substrate by welding.

Wire harness covering design

Automotive wiring harnesses are affected by various external factors for a long time in the car, such as oil, dust, friction, water-like rust, etc. If there is no protective material on the wiring harness, the wires will be easily damaged when exposed, such as disconnection and short circuit, which may causing functional failure. Several commonly used materials for bandaging are as follows:

Bellows

Corrugated tube is the most important wire harness protection material used in automobile wiring harnesses. It is generally divided into single-sided open and sealed casings.

The materials used are PE, PA6/66, PP, etc., and the temperature resistance is generally between -40℃～85℃, -40℃～125℃ and -40℃～150℃. It has good wear resistance, high temperature resistance, flame retardancy and heat resistance in high temperature areas. PA material is better in flame retardancy and wear resistance, while PP material has advantages in bending fatigue resistance.

Tape

Tape is the most widely used coating method in wire harnesses, and is mainly divided into three categories: PVC tape, flannel tape and cloth-based tape. PVC tape has good insulation properties, and its temperature resistance is generally 80°C. After improvement, it is generally only 105°C. It has poor noise reduction performance, and the wire harness is hard after the coating is completed. Currently, the VOC effect is generally poor. The base material of flannel tape and cloth-based tape is generally PET. The temperature resistance of flannel tape is around 105°C, and it has good noise reduction properties. After the coating is completed, the wire harness is relatively soft. Cloth-based tape has the best wear resistance, generally reaching D or E level wear resistance, and its temperature resistance can reach 150°C. However, the price is relatively high, and it is generally used in via holes or places with relative movement.

Braided network tube

The material of braided network tube is generally made of PA66 monofilament or PET monofilament. It generally has open type and closed type. It is characterized by very high wear resistance, but also has high noise reduction and cost. Generally used in parts with long-term relative motion.

Conclusion