Hood design-Week 2

AIM: To design hood outer panel, inner panel, necessary reinforcements and the embosses by considering the master section and design parameters.

INTRODUCTION:

In British terminology, hood refers to a fabric cover over the passenger compartment of the car (known as the 'roof' or 'top' in the US). In many motor vehicles built in the 1930s and 1940s, the resemblance to an actual hood or bonnet is clear when open and viewed head-on; in modern vehicles it continues to serve the same purpose but no longer resembles a head covering.

On front-engined cars, the hood may be hinged at either the front or the rear edge, or in earlier models (e.g. the Ford model T) it may be split into two sections, one each side, each hinged along the centre line. A further variant combines the bonnet and wheelarches into one section and allows the entire front bodywork to tilt forwards around a pivot near the front of the vehicle (e.g. that of the Triumph Herald ).

Hoods are typically made out of the same material as the rest of the body work. This may include steel, aluminium, fiberglass or carbon fiber. However, some aftermarket companies produce replacements for steel hoods in fiberglass or carbon fiber to make the vehicle lighter.

DESIGN CONSIDERATION FOR HOOD DESIGN:

• PEDESTRIAN SAFETY

Vehicle safety factors should simultaneously consider occupant and pedestrian safety, given that pedestrians are the third largest category of traffic fatalities. Most pedestrian deaths occur due to traumatic brain injury, resulting from the hard impact of the human head against the vehicle's stiff hood or windshield. Therefore, how to design a pedestrian-friendly vehicle and propose a new hood structure is a matter of urgency for minimising pedestrian head injuries. In assessing the friendliness of vehicle hoods, this study adopts the EEVC/WG17 regulations on headforms for hood tests. The finite element method is used to simulate the impact between the vehicle's hood and the headform impactor. The software used in simulation is LS-DYNA. The results predicted by the headform-hood tests show that the hood structure with aluminium-reinforced polycarbonate material provides enough absorption capability to protect pedestrians from the impacts of accidents. It is also stiff enough to keep pedestrians' heads away from the inner parts of the engine cavity. The analysis models and sandwich materials proposed herein contribute to efforts to design vehicle hood structures and pave the way for developing pedestrian protection technologies.

• HEAD CLEARANCE ZONE

Head clearance zone is the clearance such thatwhen the hood is in fully open condition it should not hurt the head of the person who is standing next to the hood. This is controlled by the opening angle of the hood. The opening angle of the hood is decided for the region of the car is manufactured. Some region may have people with average height of 5.5 ft and another region may have people with average height of 6 ft. So, deciding the right opening angle for the hood is an important criteria.

• CONSIDERATION OF NOISE, VIBRATION AND HARSHNESS (NVH)

NVH plays important role in car design. It should be designed in such a way that the noise produced by the car should be minimized. It can be achieved by using stiffners pads and mastic seals. stiffner pads and mastic seals are added in between inner and outer panel of the hood.

GIVEN DATA

MASTER SECTION

HEMMING DATA

RELIEF SECTION

PROCEDURE

• Design of Hood Inner Panel :

Inner panel is a major part which acts as a support for the outer panel. It consist of embosses which helps in distribution of forces during impact. The thickness of the inner panel is 0.75 mm as per the given data. The inner panel is created using the master section shown in the given data

• Door hood outer panel:

Outer panel is a skin of inner panel which gives a luxurious look to the car, The hamming region is created to the class A surface, Through which the outer panel is joined to the inner panel. The relief has given in the corners. Relief are provided on the surface to avoid springback situations. The thickness is given as per the data i.e, 0.75

• Reienforecment:

Whenever we add a weight to the material it looses its strenght on that area locally. To componsate that loose, reienforcements are added.

• Embosses:

Embosses will add a strengh to the material. These will help in the distributing of forces during the impact rather then directing it towards the passengers sitting inside of the car.

• Stiffner pads and Mastic seals:

These both will help in minimizing the NVH in the vehicle during motion. basically mastic seals are a rubber kind of material placed in between the inner panel and the outer panel of the hood, Which also helps in holding both together. Every mastic seals have a tendency to improve the strength locally by 80 mm diameter.

• Hemming:

Hemming is the processes where the outer panel is joined with the inner panel by adding extra material on the outer panel and made to wrap around the inner panel. The wrapping is done using the running ball rolls throught the end of the sheet.

RELIEF AT THE CORNERS

• Position striker:

For the proper opening and closing of the hood, the striker should be positioned at a correct position. The striker should be perpendicular to the trajectory of the hood. The trajectory of the hood is denoted as a circle which drawn by using the centre of a straight line which passes through both the hinge axis at their respective position.

FINAL IMAGES OF ASSEMBLED HOOD

CONCLUSION:

Hood is designed using CATIA V5 tool by understanding all the design parameters and considering the passengers and pedestrians safety.