Talking About the Design Points of Wire Harness in Vehicle Layout

Automotive Wiring Harness connects all electrical appliances on the vehicle, so the wiring range is relatively wide, covering multiple sheet metal surfaces of the vehicle body. How to design so as to avoid the risk points in wiring and assembly requires planning and analysis in the early stage of product design, so as to avoid the situation that the wire harness is squeezed and the function is damaged after loading as much as possible.

1 Preface

As an important part for connecting electrical devices in automobiles, the design scheme and implementation of wiring loom and the reliability of vehicle layout play an important role in the realization of electrical functions, which is called the nervous system of automobiles. With the increase of vehicle electrical functions and the widespread application of electronic control modules, there are more and more electrical components and wires, and the wiring harness becomes thicker and heavier. How to make the wiring harness more effectively and reasonably arranged in the limited automobile space and make automotive wiring harness play a greater role has become a problem that must be solved for Wire Harness manufacturer like Kable-X. This paper mainly analyzes and expounds the wiring design of the wire harness on the whole vehicle, and puts forward concrete and executable design methods for the positions prone to interference and wear.

2 Design Principles of Wire Harness in Vehicle Wiring

The wiring harness itself has the characteristics of softness and easy bending, and it has strong adhesiveness in layout. It is generally arranged along the front and rear longitudinal beams, round beams, parts fixing brackets, etc., and the commonly used fixing methods are wire clamp fixing and buckle fixing.

No matter what fixing method is adopted, the wiring harness will come into contact with different parts in the direction, some parts will not be affected by the contact with the wiring harness, and some parts are sporty, so it is easy to generate friction when contacting with them. How to route the wiring to avoid the wiring harness from being worn or interfered by extrusion needs to consider various factors, mainly including the following principles:

1) The wire harness shall avoid contact with the surfaces of sharp and easily worn parts;

2) The two fixing points of the wire harness should not be too tight, and the direction should be smooth without distortion;

3) The wiring harness needs to be far away from the heat source or have corresponding protective measures;

4) The branch wiring harness shall be reserved when outgoing from the main line to prevent it from being squeezed, entangled or heading in the wrong direction;

When making the wiring harness layout of the vehicle model, confirm the distance between the wiring harness and the surrounding parts according to the above requirements. If the requirements cannot be met, measures such as changing the wiring harness direction or adding protection are needed to optimize the design.

3 The Trend Design Method of Key Positions

A set of vehicle wiring harness runs through every electrical appliance in the front cabin, cockpit, chassis, doors and other positions, so the length of the wiring harness is relatively long and the distribution is relatively scattered. Therefore, all positions where the wiring harness runs need to be reviewed to assess whether it meets the requirements of the wiring harness for the surrounding space, and design methods are needed to avoid risks in key positions, which are introduced one by one below.

3.1 Waterproof Requirements -- Connection of Front Cabin Harness and Cockpit Harness

When the front cabin harness is connected with the cockpit harness, it needs to pass through the front panel of the car body. Because the cockpit is an indoor space with good sealing performance, water leakage and ash leakage are not allowed, so the wiring harness design at this position needs to consider the waterproof requirements.

Do a good job of sealing and waterproofing with the following design requirements:

A) waterproof between sheath and sheet metal; The design fit size between the via hole sheath and the front panel needs interference, and it can be completely sealed after assembly;

B) Waterproofing between the sheath and the wire harness: the inner diameter of the sheath passing through the wire harness should be smaller than the outer diameter of the wire harness to prevent water from entering from the inner diameter of the sheath;

C) Water enters the bellows of the harness: due to the layout space of the harness outside the cockpit, it is higher than the via hole sheath, and the water flows into the cockpit along the bellows. Therefore, it is necessary to guide water at the lowest point outside the cabin to prevent water from entering the inner cabin. The measures are to disconnect the bellows and change it to duct tape winding.

D) Water guide for internal wiring of the wiring harness: Because the wiring harness is covered with open bellows, water can easily enter the gap between wires after entering the bellows, and water can easily enter along the wires when the rainfall is too large. Therefore, it is necessary to add waterproof mastic between wires at the position of via sheath for sealing.

The above four points should be considered when designing the harness, and corresponding measures should be taken to seal it to prevent water from entering the room and causing carpet and other parts to get wet.

3.2 Anti-Extrusion Requirements -- The Position Where the Harness Passes Through the Sill Floor.

The laying of the wire harness along the sheet metal through the inner panel of the sill is an invisible part, so the following aspects should be considered in this position:

A) The door sill inner panel squeezes the wire harness as the only place to get on and off, and the door sill inner panel will be trampled frequently, and the resulting deformation will act on the wire harness passing through this position. If the shape variation of the decorative plate is too large, it will lead to the deformation and wear of the wire harness after being stressed. Therefore, the wiring harness in this position should be wired in a flat way to avoid squeezing the wiring harness when the interior pedal is stepped on.

B) The position of the small branch line of the wiring harness is close to the fixed point. If the trunk of the wiring harness is subjected to downward force, it is easy to cause the branch to be pulled, or it will be worn by contact with the protruding part of the ground plate, which will cause line failure and lead to functional failure. Therefore, the outlet position of the small branch needs to be changed to avoid the risk of the pedal being squeezed.

Above, if the wire harness is arranged near the moving parts, it is necessary to simulate the motion mode and amplitude of the moving parts, and if there is interference extrusion, it is necessary to optimize the direction in time to avoid risks.

3.3 Process Assembly Requirements-Wiring Harness Arrangement at Bolt Fixation

The wire harness belongs to the connecting material of the electrical parts of the whole vehicle, and it belongs to the relatively advanced station in the final assembly process. When the wiring harness is arranged and other parts are fixed, if the assembly equipment interferes with the wiring harness, there will be a risk that the wiring harness will be damaged by extrusion and lead to functional failure.

The harness runs under the seat belt fixing hole. There will be two routing modes when the harness is routed flexibly. If the harness is close to the fixing hole, there will be the risk of squeezing the harness when assembling the seat belt. Therefore, it is necessary to move the buckle position of the wire harness at this position and place it under the fixed hole. This measure can avoid squeezing the wire harness, avoid interference in design and reduce the risk of process control.

4 Conclusion

The above are the basic principles that need to be considered in the layout of the whole vehicle during the design process. In the data stage of project development, the risk of wiring harness should be considered as much as possible, and the sample line should be loaded as soon as possible to find out the points to be improved and make improvements in time. Good wiring harness layout will reduce the risk of electrical failure.