Hood design-Week 2

HOOD

Scope of Documents:

The purpose of this document is to understand the function, and design requirements of the Hood.

Also to understand the design factor & various load act on that.

Introduction:

The hood is nothing but the outer cover for the engine compartment. It is also called as Bonnet. Hoods can open to allow access to the engine compartment.

Design consideration of Hood:

1. Opening Angle.

OPENING ANGLE

The opening factor is a very important factor in hood design. While accessing the engine compartment hood will be open at a desirable angle. it did not strike the driver's head. The opening angle is varying with region to region. The person from the Japan region has a small height and the person from the USA is longer in height. The opening angle is considered in the early stage of the project.

Applicable document or norms:

FMVSS:

1. FMVSS 113: HOOD LATCH SYSTEM

This standard establishes the requirement for providing a hood latch system or hood latch systems. The purpose of this standard is to prevent the front-opening hood from flying open and obstructing the driver’s view while the vehicle is moving forward.

European standard:

1. Euro NCAP Pedestrian safety:

This standard covers all the Pedestrian safety points while collision on vehicles.

Construction:

Hood Outer Panel:

The Hood's Outer cover is nothing but the door for the engine compartment.

Material:

Aluminium Alloy, Steel

Thickness:

0.6 to 0.75mm

Manufacturing method:

Blank, Draw, Trim

Outer Panel Relief:

Relief is provided at the corner for reducing the spring back effect while doing the hemming operation.

Striker reinforcement

Material: Steel

Thickness: 1.5mm

Manufacturing process: Blank or laser cut

Hinge Reinforcement:

Material: Steel

Thickness: 1.5 to 2mm

Manufacturing process: Blank or laser cut

Hood Inner panel:

Material:

Aluminium Alloy, Steel

Thickness:

0.6 to 0.75mm

Manufacturing method:

Blank, Deep Draw, Trim, Restrike

Mastic pad Emboss:

In the above image red highlighted is the mastic pad emboss on which mastic pads are mounted. A Mastic pad is nothing but a rubber pad that is introduced in between the inner & outer panels for NVH purposes.

Please see the below image for the location of the mastic pad in the hood assembly.

While the vehicle is moving condition there is some noise & vibration happen. The rubber pad has reduced the noise & vibration between the inner & outer panels. Mastic pad are 80 mm in diam. and there is interference between the two. It acts as a joinery element between the two.

Striker position/Emboss on the inner panel:

Striker is always perpendicular to the latch. If this condition is not met, then the hood is not locked properly due to which NVH criteria are not met.

The mating point of the striker & latch should be perpendicular to the hinge axis lines. For that, the circle is created on the hinge axis and the target line is created in the striker middle of the striker. This target line is always perpendicular to that circle then our condition is satisfied that the striker is perpendicular to the latch.

Pedestrian safety points improvement:

While a better pedestrian safety rating inner panel and all the assemblies are moved down by 90mm in the engine compartment for checking the interference between the hood and the engine.

On that interference, they decide the different zone like red, yellow, and green zone. For the green zone, we removed the material from the inner panel for minimum interference.

Joining Method:

Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, improve the appearance of a part, and reinforce part edges.

Deep Draw process :

Deep drawing is a sheet metal forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch.

The process is considered a "deep" drawing when the depth of the drawn part exceeds its diameter.

h>d/2

when the deep draw is used. This is achieved by redrawing the part through a series of dies. The flange experiences radial drawing stress and tangential compressive stress due to the material retention property. These compressive stresses result in flange wrinkles (wrinkles of the first order). Wrinkles can be prevented by using a blank holder, the function of which is to facilitate controlled material flow into the die radius.

Master section:

Vehicle Interference:

1. Hood Mounting:

• The hood is mounted on a hinge. For opening & closing of the hood hinge act as a swiveling member. The hinge is mounted on the hood as well as the engine compartment.

2. Hood balancer:

1. Support Rod:

To keep the hood in open condition support rod is used. The support rod is mounted on the engine compartment or on the hood. It will be on the engine compartment when it is in closed condition & it is fixed on the hood in open condition when it is mounted on the engine compartment. It is always opposite the battery compartment for easy installation of the battery.

The support rod is always having some bends for more rigidity. But the bend value did not more than 35mm. grommet Is provided for the locking purpose when the hood is in open and closed condition. support rod design should be in such a way that there is no interference between the engine compartment and rod.

For the support rod, more energy is required for opening the hood.

2. Gas stay rod:

A gas stay rod is used when the hood assembly weight is more than it will be helpful for the opening of the hood. The gas stay rod required minimum force for the opening of the hood.

For gas stay rod mounting additional bracket is used which acts as a reinforcement.

Testing:

Pedestrian head Protection performance tests:

Car accidents in which pedestrians are hit by cars moving at a certain speed and their heads collided against car bonnets or front windshields are assumed. An adult or a child pedestrian’s head simulated impactor (head impactor) is projected toward the car bonnet, etc., from the testing machine. The impact received by the head impactors is measured and then evaluated using the head injury criterion (HIC).

As per the previous test data, Euro NCAP makes the child impact zone & Adult impact zone as shown in the below image.

For better pedestrian rating the hood is moved down by 90mm and check how much area is interfering with the engine compartment. According to that interference the following zone is made as shown in the below image.

The main focus of hood engineers is to achieve a greener zone on hoods so the rating is more for the car, for that they remove more material from the inner panel.