The automotive wiring harness is referred to as the central nervous system in the vehicle. It mainly consists of an electrical harness and the mechanical harness in the design. The current project is focused on the mechanical wiring harness and its rules and procedure to be followed while routing in the virtual condition. CATIA V5 electrical workbench is used as the CAD tool for routing the wires in the engine and tailgate components.

Some terms need to be understood before designing the wiring harness.

 Basics of the electrical distribution system and wiring harness

Electrical Distribution System (EDS):

                                        It deals with physical (location of electronic components placed in the vehicle, front end to back end) and logical (different Electrical Control Units) architecture, schematic development, power distribution (set with fuses to check wiring harness is safe in various failure modes), wiring harness design and wiring harness component design of given electrical system.

E & E Architecture: 

                     It is a high-level logical connectivity diagram representing the number of systems, sub-systems, and logical connections between them. It is also extended to show the CAN (control area network) network between different electronic controllers.

Logical schematics:

                     It is detailed design of E&E architecture which is extended to show the logical connectivity between different components and controls of different systems and sub-systems.

Electrical schematics:

                         It is detailed design of logical schematics, which describe the pin-to-pin connectivity, properties, fusion distribution, grounding distribution, wire properties (wire type, colour, gauge), interconnects, circuit properties (circuit numbers, connector designation numbers, control device number), specification of component (rating od diode, resistors) etc., This is the end design of electrical core design of system and used as primary input for harness development.

Wiring harness topology:

                      It is strategy to divide the harness between different pieces to achieve the best manufacturability, serviceability and cost-effective design.

Ex: engine harness, door harness, til gate harness.

Note: Wiring harness cannot be repaired. It is advised to replace the damaged wiring harness parts.

Wiring harness routing:

                         It is the desired path of wiring harness into given vehicle environment by applying set of design rules and industry best practices.

Wiring harness packaging:

                         Deals with the fixing/mounting strategy of wiring harness routing to ensure the safe, reliable and durability of wiring harness by applying set of design rules and industry best practices.

Virtual environment: 3D representation of vehicle components.

Benefits: 1) Huge cost saving, 2) Fuse failure avoiding, 3) Easy to predict i.e., warning in harness

Wiring Harness Terms

Wiring harness is the assembly of different systems, sub-systems in the vehicle. It won't have any function; it depends on its system and sub-systems. It used to pass the signals between components.

       Wires:

Wiring harness consists of various wires bundled together, with each individual wire responsible for carrying electric signals and energy used ins tarting the engine, lights, meters, navigation system, Power windows and doors, and other devices in the vehicle. Wires are Cu conductors insulated with PVC insulation. Initiative in the industry to use the Al wire to get the benefits of weight and cost reduction.

Connector:

An electrical connector, is an electro-mechanical device used to join Electrical termination and create an electric circuit. Electrical connectors consist of Housing, Terminal, Wedge Locks, Seals, Cavity, Mounting Cam etc., Connectors are plastic moulded housing with locking and retention features.

Terminals:

Terminals are defined as "A device designed to terminate a conductor that is to be affixed to a post, stud, chassis, another tongue, etc., to establish an electrical connection." Terminals are metal (brass) conductor with plating (tin, silver, gold) constructed in specific shape to secure the joint from environmental conditions and with minimum electrical resistance.

Protection device:

• Corrugated flexible tubes also known as Cot Tubes / Convoluted Conduits have a wide range of application in automotive industries.
• Corrugated tubes are made from plastic material and they are flexible.
• Theses tubes are used to protect the harness from thermal and physical damage, sometimes to improve harness appearance.
• Protection covering are flexible, temperature, wear and tear resistant moulded plastic/polymer parts.
• Sealing Grommets are used mainly for three purposes. Sealing, Protection and to absorb vibration/shock.
• Protection Grommets are rubber moulded components used in wiring harness for protections.
• Insulations are adhesive/non-adhesive tapes and sleeves. They are made from PVC or cotton/polymer material. Cotton tape in high temperature area (engine)

Clips and clamps:

Wide variety of clips and clamps are available to mount the wiring harness.

Fuse and relay box: are plastic moulded parts used to package Fuses and relays in systematic manner. It also protects them for any damage (Physical and Environmental).

Retention device: are plastic moulded parts to mount connectors and other harness components. (Connector mounts, secondary locks, connector back shell etc). Primary locking is provided by the terminal itself; secondary locks are not mandatory but there are used to ensure that there is no damage. Back shells are the packaging devices which are used at the end of the connectors. It guides the wire to the connector in a constrain packag ng area or to provide the better appearance at the end of the connector.

Guiding channels: are plastic moulded or metal parts designed to guide harness bundle in given geometric area to secure and protect the harness.

Electronic components: Diodes, terminating resistors, Flasher, Timer circuits are sometimes part of harness support

Logical Architecture,Electrical Schematics and Physical Architecture are designed by the electrical department whereas harness Routing and packaging is developed by mechanical department. Upon integration of electrical and mechanical departments final harness drawing is designed.

• Wiring Harness Design Process

ELECTRICAL PART DESIGN;

Geometry Parameters

 Points and co-ordinate system (axis).

Connector connection points 

This point is used for the connection of one connector to another connector.

Harness bundle entry point —

This point defines where the harness bundle segment point will end when routed to the electrical connector. Cavity connection point (optional): This point is used to define the connection of a connector to a connector clip. This only applies to connectors which have the mounting feature for a connector clip.

Once the bundle and connector entry points and axis system are created in part design workbench as shown in Fig. 17, switch to electrical part design workbench. In electrical part design workbench click on Define Connector option and click the connector and enter the type, name and number of terminations.

After that bundle connection and connector connection as per the required side of connectors,

1.First select the face for representation

2.Second select the point for bundle connection point

3.Slect again the face for intial face oof bundle.

CONNECTOR CONNECTION ;

1.First select the face for representation

2.Second select thecontact point for connector connection point

3.Slect the coincidence axis of yaxis

4.And slect the orientation of z axis

 FUR TREE CLIP;

Draw a point for to creata a plane 

A plane is used to define the entry and exit point of the wiring branches

After that we move to electrical part design work bench and define the part as support part by using the command of define support part

In this we mention the first plane is also known as entry plane after the second plane has to define for exit plane atlast define define the base plane as a neutral plane

• PREPARATION OF HARNESS ASSEMBLY

The harness Context Assembly:

This is the top-level product file that contains the harness Geometrical Bundle/Assembly and the wire harness electtical bundle.

Geometrical Bundle:

This sub level product file is the wre harness product that contains all of the harness components i.e., clips, supports, connectors, splices, grommets, annotation and actual physical bundle segments and branches.

 Geometrical Bundle:

Geometrical Bundle is the important file that sets the wiring harness in the correct position. Any part selected wrongly in it can lead to damage the wiring harness.

Now convert the Assy_Ceometrical_Bundle into the electrical assembly file. The Wiring harness context will be same so as the surrounding CAD files can be added which is used for the review. Geometrical Bundle can also be act as main assembly product file in case of harness context is not necessary.

Switch to electrical harness assembly workbench and select the Geometrical Bundle command in it. Then select the Assy_Geometrical_Bundle product, the symbol of it changes to electrical harness assembly symbol.

Ensure that all harness components that are needed in Assembly are Electrically defined With all required parameters before adding them in assembly.

Multi Branch able

TO create the multi branch able file. First ensure that all the components are electrically defined and placed in the correct position.

Switch to the Electrical Harness Assembly workbench. Click Multi Branchable definition just below the Geometrical Bundle command. Once you click it, Multi Branchable is added to the product file.

In Build Mode, Mode options can be Slack, Length, Bend and Straight Bend. If slack is provided the bundle length will be increased according to the slack and the bundle will be easily routed. If length is provided, then CATIA overrides the calculated length of the bundle and adjust the bundle with the length given. In bend mode, the bend radius will be taken and the length will be calculated accordingly. In straight bend, bend radius will be neglected for the length calculation or it is kept minimum.

In Route Definition, only electrical components parts will be considered but with few changes non electrical parts will also be considered.

 Create bundle selection separately. Do not select all the bundle selection at once which are in line with the branch.

To add a branch point to the main bundle and extend the bundle from the branch point, in Multi branch able select the Add Branch Point Command and select the bundle segment on which the branch point needs to be added.

 

 Clearance Management;

• Clearance management basically focus on the wiring harness clearance With the surrounding parts.
• This is primary requirement for the routing and packaging.
• Clearance management should be conducted in CAD software or visualization software.
• It is also known as DMU (Digital Mock up).
• This study is part of geometrical integration.
• Clearance requirement varies between industry to industry. However, the requirements can be used to understand the basics of clearance management 
• IP Rating- Ingress Protection Rating:
• IP ratings are defined in international standard EN 60529 (British BS EN 60529:1992, European IEC 60509:1989). They are used to define levels of sealing effectiveness of electrical enclosures against intrusion from foreign bodies (tools, dirt etc) and moisture.

 

Harness branching rules;

• Branch length should be minimum 50 mm.
• Minimum distance between clip and nearest branching point should be 25 mm.
• Minimum distance between two breakouts should be 50 mm.
• Limit the number of branches from single branching point to 4.
• If there are multiple branches routed from branching point for identical connectors, then connector connection Poka-Yoke should be achieved by harness dressing and managing lengths to avoid incorrect connections.
• Ensure that harness protection is provide according to surrounding temperature, manufacturability and expected reliability.
• Always keep the harness connector at height than harness routing and branching points. This is to ensure that gravity does not allow water entry through harness bundle.
• Use of plastic guiding channels are recommended to meet the clearances in critical areas if it is difficult to achieve by use of clamps. Ex- Inject harness routing on engine.

 

 Steps to be followed

Step 1: create a new product file and rename it as Assy_Engine_Wiring_Harness_Context

In the name of CONTEXT ASSEMBLY

Step 2: Now copy and paste the TAIL DOOR assembly file to the context assembly.

Step 3: Create a new product under context assembly and rename it Geometrical_Bundle.For this we need to create two geometrical for tail lamp and number plate lamp seperately

Step 4: Import all the required connectors with electrical properties into the Geometrical bundle.

Step 5: Place all the connectors in the specified locations of the engine using snap tools.

Step 6: After placing all the connectors, it is required to locate the interconnection connector.

 It is advised to use already drilled bolts for placing the interconnection connector and not to drill any holes to the engine exhaust manifold as it leads to damage of the engine.

Step 7: Addfur tree clips to the context assembly and not to the geometrical bundle assembly because they are fixed at the manufacturing line. If fur tree clips are supplied with the wiring harness then it can be part of geometrical bundle assembly.

Step 8: Now switch to Electrical harness assembly design and select the geometrical bundle command and select the Geometrical_Bundle.

The icon of the assembly converts to bundle.

Step 9: Start the routing. Start from the interconnection connector.

Step 10: Considering all the harness packaging rules, the harness for the engine is routed.

Figure : Wiring Harness Routing.

Step 11: Check for bundle continuity. All the bundles are fully connected.

 

 

Flatten the harness assembly;

For flattening the harness assembly open the harness flattening work bench 

In that we have to select the flatening parameter command

after that we choose the parameters of flatening in  that  dialog box

After that to add the harness assembly click the command called extractby using this add the harness routing file 

And select the command flatten to covert the harness routing into harness flatten

after slecting this select all the branches to be flatten

like this will come then click ok ,after that our harness flatten will get

CREATE 2D DRAWINGS;

Open the work bench called drafting 

to add the drawings selsct the front view command

and select the face were we need like that

and add the file in drafting