Challenge

BiW Hood with N CAP regulations

AAbhishek S24 Jun 2021

OBJECTIVE

To create an Opening body panel (i.e. Hood) that covers the Engine compartment while passing in:

Frontal Crash Test
Pedestrian safety
Dissipate forces outside the car body.

DESIGN PRINCIPLES

Sl. No.	Design Considerations	Description
1.	NVH	The Outer and Inner panel should be well joined and sealed. The Latch should firmly lock onto the Engine compartment.
2.	Hoodstay Mounting	Designing the Mounting for either of the 2 Hood balancers: Support Rod Gas Stay
3.	Latch and Striker point	Opening and closing trajectory of the hood.
4.	Hinge Axis	The axis point should be well within the Centre of Gravity of the Hood to support its self-weight in the opening position.
5.	Deformable Bracket	Include Deformable Brackets during a collision to ensure pedestrian safety.
6.	Euro N-CAP Assessment	Head Impact Test Child Head Impact Adult Head Impact Upper Legform to Bonnet Leading Edge Test Legform to Bumper Lower Legform to Bumper Upper Legform to Bumper
7.	Pedestrian Rating	Plot the regions for the Adult and Child Head Impact zone. Design the Inner panel to reduce the rigidity and forces get distributed sideways. Desired outcome: Child Head Impact zone: 1000-1500 WAD Adult Head Impact Zone: 1500-2100 WAD

PROCEDURE

STEP 1: PRELIMINARY STUDY

Before working on the Hood, we need to ensure that the Hood is feasible for the market. We study for:

Sl. No.

Criteria

Description

Visual Representation

Type of Hood

We decide on the type of Hood for a better pedestrian rating.

Inlaid Hood: The endpoint of the car lies on the Fender.
WAD (Wrap around Hood): The endpoint of the car lies on the Hood.

Headzone for Locker Striker

The Head shouldn't hit the hood when reaching out to the engine/battery, etc.
And also, the person's hand should be able to reach the hood for closing.

Hood Opening Angle = 55-68 degrees

The value varies from region to region, depending on the average height of the citizen.

Hood Balancer

A mechanism that holds the hood open.

Support Rod

Mounted either on the Hood/Engine.
Simple and cost-effective.
Used on commercial cars having a lighter hood.

Gas Stay

Pneumatic press or Actuators.
Needs no manpower but is expensive.
Used on performance cars having bigger/heavier hoods.

Support Rod	Gas Stay

Pedestrian Head Impact Zone

After getting skin data, we'll refer to:

Side Reference plane
WAD

We plot the regions for the Adult and Child Head Impact zone.

Predesign

We offset the hood by 90mm inwards (towards the cabin).
There will be interference with the engine compartment.
- Interference `uarr` `=>` Red Zone
- Interference `darr` `=>` Green Zone
We start giving gaps in the inner panel so the rigidity decreases during head impact and the pedestrian is safe.

STEP 2: INPUT

We get the Class A surface with predefined edges from the Styling Team.
We get a Master Section as well, which is a predefined sketch that is adaptable to different situations.
As Design Engineer, we check for the initial feasibility and whether the part has to be raised/lowered.

Note: We don't have reference data like the engine compartment, we can go ahead with designing the engineering features.

Add/Create the parts (Input Class A, Hinge and Striker) to the new assembly:
- Hood Inner Panel (Create Part)
- Hood Outer Panel (Add Part)
- Hinge Assembly (Add Assembly)
- Striker (Add Part)

STEP 3: MEETING THE SAFETY REQUIREMENTS

Requirements

Problem

Solution

Pedestrian Safety

If the Hood is too rigid then the pedestrian will suffer from a severe head impact during a collision.

Make the Hood lighter and thinner while maintaining the same strength.
We introduce an Inner panel with reinforcements.

Passenger Safety

During a frontal crash, the stresses travel straight into the cabin.

Create Emboss along Y or V directions for the forces to be distributed sideways and onto the Crumple zone, that is,

Shot Gun
Rail
A-Pillar

Offset class A surface by 25 mm to meet the Pedestrian safety requirements.
Provide a 40mm width for the offset and open the part by 45 degrees to provide Deep Drawing conditions.
Take another offset of 10-15 mm and further to 5-6mm.
These Offsets create Emboss that satisfies 2 applications:
- Removing material and making it lighter.
- Adding strength by functioning as a reinforcement.

Design Rules to be followed to meet Manufacturing standards:

Draft Angle	Facilitate Deep drawing conditions for the sheet metal. Minimum 10 degrees outer draft.
Emboss spacing/clearance	To facilitate Tool actuation while drawing. Minimum 5mm gap between the embosses lying on the same surface.
Clearance for Material removal	To facilitate Blanking for material removal of the sheet metal. Minimum 3mm gap to give clearance for the Punching tool.

Functions performed for creating the Emboss on the Inner Panel:

Offset surface	It creates an Offset of the selected surface and projects it in the vector direction perpendicular to the surface. Note: The Offset dimension is limited up to the Radius of the surface (if curved). But if the surface is complex then it gets distorted from a far distance, well within the limit.
Offset curve on surface	Creates an offset of the edge onto the corresponding surface. Fillets are automatically provided to avoid sharp corners. Note: Ensure the curve gets, Trimmed to face edges, if it is extending beyond. Extended to face edges, if it is falling short.
Trim sheet	Lets us trim the Target-face/body with respect to a cutting boundary(curve/surface/plane).
Through curves	Helps to fix small patches by providing smooth transitions.
Law extension	Creates an Extended surface/sheet from a section and a reference plane/direction.
Emboss	Creates an offset of any desired shape/section from the corresponding plane. This command vital for providing reinforcements for the sheet metal component.
Face blend	Joins 2 faces/bodies having separate edges.
Edge blend	Joins 2 faces of the same body/object bound by a common edge.
Sketch Tools	Helps us draw a line/spline/arc/rectangle in the Datum plane/flat surface, about the geometry features. The Result is a Curve on a specified datum Plane.
Project Curve	Projects the sketch features onto any Datum plane or Surface (even curved). Note: We cannot sketch on a curved surface. Therefore, we sketch on a datum plane and project it onto the respective surface to get an accurate section of the sketch.

STEP 4: HOOD OPENING (ABOUT HINGE AXIS)

Conditions	Description
Opening angle	55-68 degrees
Hood Balancer	Close to the Centre of Gravity (Triangular region joining Hinge Axis and Striker Locking point) .

Design Principle to be followed:

The Hinge position is correct when the Striker is exactly perpendicular to the trajectory at the local region.

Take the Opening position of the Hood and hold the Hinges tentatively, along a straight line.
The straight line is the Hinge axis. Now we have 3 inputs:
- Hinge axis point (Centre point of Hinge axis)
- Master Section (Predefined)
- The concept from the previous vehicle (We don't have so we go with our own design)
From the input, we get a predefined Triangular area that is exactly over the Centre of Gravity, and we validate if it is right.
The Height of the Triangle is determined by the radius of the circle drawn perpendicular to the Hinge axis.

R= Centre of Striker to Hinge Axis axis point

We can infer the circle to be the trajectory of Hood closing and opening.

Move Component	Allows us to translate/rotate the geometry with respect to the assembly's common Datum Csys.
Assembly Constraints	Allows us to arrest or introduce any relationship between components of the assembly. Note: we have to Fix the Inner and Outer panel before working on them.
Datum Plane	Creates a flat plane in the Datum Csys.
Sketch	Create the desired shape/section on a plane/flat surface.
Emboss	Creates an offset of any desired shape/section from the corresponding plane. This command vital for providing reinforcements for the sheet metal component.
Edge/Face Blend	Face Blend joins 2 faces/bodies having separate edges. Edge Blend joins 2 faces of the same body/object bound by a common edge.
Point	Helps us create with respect to any relationship from the geometry. For example, we create a Hinge axis point from Ellipse/Curve/Circe option while selecting the Hinge Engine Compartment cross-section.
Curve	Creates a line/spline/arc/rectangle in the Datum Coordinate system, with reference to the geometry features.

STEP 5: STRIKER POSITION

In the Inner panel, draw a constrained Circle and a Tangential line.
Constrain the line by introducing an angular relationship of about 80 degrees with a horizontal construction line.
In the Striker part, move the component as close to the local region and the tangential line of the circle.
Create a Datum Csys (Coordinate system) at the top edge of the striker. Ensure that the X-Y-Z orientation is similar to the Assembly Datum Csys.

Draw a perpendicular line from the centre of the latch point and ensure sketch constraints.
Finally, Assembly constraint the Perpendicular line with the Tangential Line drawing in the Inner panel part.
Change the Angle of the Tangential line to adjust the position of the Striker on the Inner panel.

Note:

This adjustable angle in the circle represents the trajectory of the Striker with respect to the Hinge axis point.
As a result, we have determined the Opening and Closing trajectory of the Hood.

STEP 6: JOINING INNER AND OUTER PANEL

Both the panels are joined using the following design attributes:

Hemming	Extend the Class A edges. Bending and Twist. Rollers are used up to 3 passes to ensure proper pressing. Predefined Nomenclature 2mm Gap between the thickened Inner and Outer Panel.

Mastic Sealants	It is a hard rubber that acts as a glueing agent between the Inner and Outer Panel. When it gets into the hot bath in the furnace, it gets hardened joining the 2 panels. Application Every sealant has the capacity to strengthen the component within a radial range of 80mm around it. Reduces the NVH levels. Predefined Nomenclature 5mm Gap between the thickened Inner and Outer Panel to accommodate the Mastic.	Note: The Mastic sealants are just a visual representation to show the strengthening and joining capacity.

Corner Relief	When passing the Rollerball, the sheet could vibrate due to the Spring back effect. The CAE team studies if the force lets the panel retain its original shape. The Red/Dark zone is the region where the change in shape occurs. They occur in the corners, to avoid that we provide some relief to the hemming so that ball does not fully roll on the corner.

RESULT

We have attained the Hood assembly that meets the respective design standards.

NVH	Reduced NVH using Mastic sealants.
Latch and Striker point	The Striker is exactly perpendicular to the trajectory at the local region.
Hinge Axis	Provided the Opening and Closing Trajectory for Hood, about the Hinge axis.
Pedestrian Rating	Designed the Inner panel to reduce the rigidity and let forces get distributed sideways during a collision.
Euro N-CAP Regulations	The Inner panel was designed taking the following into consideration: Head Impact Test Upper Legform to Bonnet Leading Edge Test Legform to Bumper

BiW Hood with N CAP regulations

Ship work like this
in your own course.

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Ship work like thisin your own course.

Talk to a career counsellor

Ship work like this
in your own course.