DESIGN FOR WIRING HARNESS FOR THE BACK DOOR OF A CAR

DESIGN FOR WIRING HARNESS FOR THE BACK DOOR OF A CAR

Back Door is the rear BIW closure component of a car. Back door or the tail gate is considered the fifth or the third door of the car. It can swing vertically like in hatchbacks or sideways like in SUVs and minivans. The term Tail gate is generally used for the closure component of trunk for sedans and coupes.

Introduction

The back door houses many electric components and sensors such as tail lamps, rear wiper motor, brake lights, name plate light, reverse camera and sometimes proximity sensors as well.

To route the wiring harness, we need to k now the positions of the connectors; for this report, we have to assume the mounting positions of the connectors for these electric components.

The wiring harness connects from the roof to the top of the back door as it is a vertically swinging back door, for a side swinging back door, the wiring harness would connect from a side.

DESIGN PLAN

To come up with a design for the wiring harness, we need to plan the layout of the wiring harness. We need to incorporate all the connector position and planned bundle routes in the plan, we will proceed to designing the wiring harness using this plan.

(Plan of the wiring harness)

The rear door wiring harness originate from the connector from the roof, an interconnecting connector is used to connect the back door wiring harness to the main harness line. For the interconnecting connector, we use a 12 pin interconnecting connector, ample slack is provided in the first branch so that the door can swing easily without any tension on the harness bundle.

The harness is then split into 2 branches, one going to the top brake light connector another branch to be routed down following the inside of the sealing flange to the rest of the components.

From an intersection shown, the wiring harness is further split so that one branch moves down to the tail lamp and other moves sideways to the name plate connectors.

The name plate lights and wiper are connected with sub branches and the main line is then routed to the remaining tail lamp.

Design Considerations

The wiring harness around the back door is routed keeping these considerations in mind:

<!-- [if !supportLists]-->·         <!--[endif]-->The distance of the edges of the door from the wiring harness should be a minimum of 50mm.

<!-- [if !supportLists]-->·         <!--[endif]-->Distance between two clamps on a straight branch should be mot more than 200mm.

<!-- [if !supportLists]-->·         <!--[endif]-->The minimum branch length should be 50mm.

<!-- [if !supportLists]-->·         <!--[endif]-->The distance between a clip and the nearest branching point should be a minimum of 25mm.

<!-- [if !supportLists]-->·         <!--[endif]-->The distance between two straight connection points should be a minimum of 200mm.

<!-- [if !supportLists]-->·         <!--[endif]-->The bend radius ratio should be 1.4 times the bundle radius.

<!-- [if !supportLists]-->·         <!--[endif]-->All the bundles should be fully connected.

Design Methodology

The Design Process is done in following steps:

Step 1: Downloading and defining the wiring harness components as electrical equipment.

An interconnection connector with 12 pins is used for initiating the routing of the back door wiring harness. A 4 pin connector connects to the tail lamps and wiper motor connections. For the top brake light and the name plate lights, a 2 pin connector is used.

The geometrical properties of the connectors is first defined: The bundle connection point and the connector connection point along with the connector connection axis. The component is then defined electrically: Connectors are defined with the connector connection and bundle connection properties. The clips and clamps are also defined as electrical parts. Lastly the protective coverings are created and added to library. For this report, we use 10mm and 5 mm bundles, so we use 15mm and 10mm cot tubes.

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(Defining Geometrical properties of the connector)

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(Defining electrical properties of the connector)

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(Defining component as connector)

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(Cutting the sealing flange for grommet insertion)

Step 2: Setting up the back door and wiring harness assembly:

The back door assembly file is converted into skin data which is used to mount the wiring harness components. This is done to save computation time and memory. A product file is created as the wiring harness context assembly and the backdoor skin data is saved in the same product.

Another product file for wiring harness bundle assembly is created, the wiring harness components will be stored in this assembly: The clips and clamps, connectors, protective covering and the multi branch-able will be a part of this assembly.

Step 3: Manipulating the connectors and mounting electrical equipment’s to appropriate positions:

The connectors are added to the wiring harness bundle assembly and moved and rotated to their appropriate connection positions. Recurring connectors are copied and pasted and translated to their respective positions. The positions need not be absolute as this will just be an initial design concept.

The 4 pin connectors are positioned near tail lamps and wiper motor. The 2 pin connector are placed near brake light and name plate lights. The interconnector connector is mounted over the sealing flange through which all the branches of the backdoor harness bundle originate.

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(Electrical devices placed on their proper position)

Step 4: Adding Fir tree clips from routing the harness bundles.

The fir tree clips are added to the wiring harness bundle assembly. The design rules, considerations and best practice are followed to ensure the best routing of the wiring harness.

Step 5: Routing the multi branch-able harness:

The Multi branch-able is originated from the interconnection connector and through the fir clips, the bundles are routed to the different connectors. Proper bundle diameter is ensured and the bend radius is kept a minimum of 1.4 times the bundle diameter. All the connectors are connected using multiple branching points emerging off the main branch. Slacks are applied in the bundles to route the bundles properly.

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(Routing the wiring harness)

Step 6: Checking the Electrical continuity of the bundle:

The electrical continuity of the bundles is then checked using the Search command in CATIA; Search> Advance> Electrical WB, Bundle Segment type, fully continuous; Check for both true and false. For True, all branches should be shown and for false, no branches should be shown.

<!-- [if gte vml 1]> <![endif]--><!-- [if !vml]--><!--[endif]-->(Checking electrical connectivity)

Step 7: Adding Protective covering:

Slit corrugated tube is added to the exposed bundles the end connection clearance is given as 30mm.

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(Protective cover)

Step 8: Wiring Harness Flattening:

The wiring harness is then flattened using the Electrical Harness Flattening WB. Create a new product file for the flattening in the flattening workbench and define the Harness Flattening Parameters, save it in the same folder with all other files of back door harness project and then extract the geometric bundle from the wiring harness context product file. Then using the flatten command flatten the harness by selecting all branches to flatten. Manipulate the flat harness as required for the drawing and save. Open a drawing file and create a 2D representation of the wiring harness.

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(Flattening wiring harness multi branch-able)

This concludes the design of the wiring harness for the Back Door.