Hood design

HOOD DESIGN

Aim: - To Design and assemble the Car Hood/Car Bonnet Inner panel

Here we are going to understand What Is the Hood/Bonnet? What are the Materials Used toManufacture the Hood? What are the Design considerations?

About Hood/Bonnet
The hood or bonnet is the hinged cover over the engine of motor vehicles that allows access to the engine compartment, or trunk for maintenance and repair.
On front-mounted engine cars, the hood may be hinged at either the front or the rear edge, or in earlier models, it may be split into two sections, one on each side, each hinged along the
centreline. A further variant combines the bonnet and wheel arches into one section and allows the entire front bodywork to tilt forwards around a pivot near the front of the vehicle.

Materials Used

Hoods are typically made of the same material as the rest of the bodywork. This may include steel. aluminium fiberglass, or carbon fibre. However, some aftermarket companies produce

replacements for steel hoods in fiberglass or carbon fibre to make the vehicle lighter. Before we dive into the design, let us understand the rules and regulation standards for designing the hood.
● A perfect hood design means it should have a great impact distribution angled outside the car.
● In Japan and Europe, regulations have come into effect that places a limit on the severity of pedestrian head injury when struck by a motor vehicle. This is leading to more advanced hood designs, as evidenced by multicore hood inner panel designs.
● European Enhanced Vehicle-Safety Committee (EEVC), European New Car Assessment Program (euro NCAP)

Design consideration

While designing the hood we should have to focus on the Pedestrians safety, Occupant Safety, opening angle, vehicle quality, etc.

Pedestrians safety

Pedestrian safety is one of the important criteria which must be taken into consideration during designing a hood. Based on the wrap-around distance and pedestrian head impact zone, the hood is designed so that during a collision impact on the person must be reduced. Around the impact zone, the hood is made softer by removing material. There are two main zones in the hood that are considered while designing it. The Child head impact zone (1000mm to 1500mm) and the Adult head impact zone (1500mm to 2100mm) as shown above. The wrap around distance is the distance from the ground level to the end of the hood. The side reference line and the wrap-around distance are related to each other. If the side
reference line is on the fender, the wrap-around distance will be more and the impact zone will be less and vice versa. Pedestrian safety is to avoid severe injuries to the head, the high impact area for adults and children is subjected to less thickness. In addition, no reinforcement should be provided in that area as, during the head collision, the hood will absorb the head impact energy leading to collapse of the hood and thus protecting the severe head injury. To protect the occupants inside the car during the front collision, the design of the hood should be in such a way that the force should travel in the upward direction through the embossed and directed towards the body of the car during the collision. Thus, protecting
the occupants inside the car. Mastic sealants and embossed help to meet pedestrian safety standards. The adult and child impact zones are taken into consideration, and the deformation zone considered with respect to the engine compartment and outer panel thereby determining the interference. This generated deformation is considered critical and needs to be relocated or tuned to fill. Relocating or tuning leads to reduce the force exerted on pedestrians especially in heat during collision Generally, inner and outer panels are made of 0.65 to 0.75mm thick and reinforcements are made of 1.5mm thick. Adding more reinforcement improves the strength but also increases the cost and weight of the car

Opening angle

Head clearance zone is the clearance such that when the hood is in the fully open condition it does not hurt the head of the person that 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 the car is manufactured. Some regions may have people with an average height of 5.5 ft and another region may have people with an average height of 6 ft. so deciding the right opening angle for the hood is an important criterion.

A hood stay is a device that is used to keep the hood in an open position. there are two types of hood stays 1) Support Rod 2) Gas Stay

Support Rod

The support rod is usually inside the engine compartment, when we open the hood and keep it in open condition, one end of the support rod attaches to the hood and supports it. this support rod has to be fixed manually onto the hood. The design of the support rod is not linear but it should have some bends to increase the rigidity and strength of the rod. the support rod should be mounted such that it does not collide with other parts, also the support rod should be mounted on the opposite side of the battery to avoid

Gas Stay

A gas stay is used to open the hood, keep it in an opened state and then closing the hood. This is an automatic process, that is the gas stay uses an actuator to open and close the hood. one side of the gas stay is mounted on the body side and the other side is mounted on the hood. gas stays for the front hood are mainly used in high end performance cars.

Components of the Hood/Bonnet

Outer panel:
The outer panel is actually called the skin of the vehicle which is designed by the styling team to get a good look for a vehicle by covering the inner panel and engine parts of the car. This part should not be welded to the inner panel but using the sealant and mastic points makes contact between the inner and outer panel which acts as a bond between both and makes the hood stiff.

Inner panel:

The main part of the hood which gives support to the outer panel of the car and with its embossing shapes dissipates the force in different directions when the vehicle takes crashes to not to injure the men in the car.

Latch/striker

It is a part that helps in locking the hood with the striker which is mounted on the engine block when it is not in use. It plays a major role in opening and closing hood for maintenance of car engine and gives a tight locking position not to create undisturbed noises when the vehicle is running.

Hinges:

The hinge consists of two parts- hinge at the inner panel and hinge at the engine compartment. This coupling allows the hood to open and close, as well as makes contact between the engine block to the hood. It also controls the lifting of the bonnet mitigates the consequences of a collision between a pedestrian and a vehicle.

designing hood

given input

we will do work on half of the part and then symmetry for other side because both sides are same

for that splitting the given part

offsetting the split part 2mm

taking boundry to the offsetting part

taking parallel curve

extruding parallel curve

giving edge fillet for the sharpe edge

splitting the outside part

again offset base part 4mm

taking boundry, parallel curve 22mm,extrude, edge fillet 35mm, and split

and same for next part

we get the output

joining the space between the two parts by using multi section

for that we have to take boundry for both edges and smoothcurve for boundry

then doing multisection

giving fillets for both edges

again offseting base part 25mm

taking boundry, parallel curve 50mm, extruding parallel curve and giving edge fillet

then spliting the part

again we need to join the gap by using multisection

for that we have to take boundry for both edges inside and smooth surve for boundries

then go for multisection

next fillets for the edges

drawing sketch on zx plane and projecting on to the surface

spliting the part

using sweep

offseting base part 20mm and trimming the part

giving fillets for the edges

creating emboses

drawing sketches saperately and projecting on to the surface

spliting each sketch

sweep the edege of the split part

offseting base part 15mm and triming the part

same procedure for all the sketches

next fillets for all the edges

creating mastics

projecting all the sketches on to the surface saperately

then split each sketches saperately

creating emboss for hinge

draw a sketch and project

split the part

extruding the boundry and trim the part by using another extrude

fillets for the edges

creating emboss for striker

projecting on to the surface and split

extruding the boundry and trim the parts

fillets for the edges

taking reference of the hinge create holes

project and split saperately

taking reference of latch and create holes

project and trim saperately

symmetry to the other side and join

make thick surface

now work on styling surface

offset

create boundry and parallel curve

split the part

sweep the edge

trim extra part and give wdge fillet

creating relief rear section

after projecting both sides split the part

creating thickness

relief rear section

assembling hood, hinge, striker

fixing the main part

striker

fix all the degrees of freedom

hinge

fix all degrees of freedom

mirror to other side

opening angle

final froduct