Hood design-Week 2

Aim: To design a car hood in understanding with mechanisms behind the hood design by considering the safety of the pedestrians.

Tasks: Hood is not as simple as we see it from outside, t consists of many parts. We need to perform the tasks mentioned below to design the hood.

1. Design the inner panel of the hood.
2. Design the outer panel of the hood.
3. Join the inner panel and outer panel by hem.
4. Create emboss structures for the force distribution during impact.
5. Add reinforcement (Latch, Hinge)
6. Positioning of hinge and latch.
7. Mastic positions.

Inputs Provided: Several inputs Hood thickness information’s are provided.

Master Sketch:

Hood thickness data:

• Outer Panel Thickness = 0.75mm
• Inner Panel Thickness = 0.75mm
• Reinforcement Thickness = 1.5mm

1. HOOD

The Hood which is also called as Bonnet, which is also the cover for engine compartment. Bonnet is main component of a car at the front portion. It is used to decorate the car and add luxurious look. The shape of the bonnet is made aerodynamic in order to minimize the air effect. Bonnet is generally used to access the parts easily such as radiator, engine and many other parts. It is a critical component because of frontal crash and pedestrian’s safety. It also helps in dissipating the heat from the engine to outside rather than sending it again inside.

The work has been done on the hood design of the vehicle front end to reduce the injuries to the pedestrians in the event of a pedestrian vehicle collision. The front portion of the vehicle gets damaged including bonnet when met with an accident. The bonnet system is an access panel to the engine compartment to enable maintenance of power train, drive belts, battery, fluid levels and lamp units. It is fundamentally a reinforced skin panel with many safety and quality requirements.

1.1 Purpose of the Hood System

• The bonnet system is an access panel to the engine compartment to enable maintenance of power train, drive belts, battery, fluid levels and lamp units.
• It is fundamentally a reinforced skin panel with many safety and quality requirements.

Fig: Hood (Hyundai)

Fig: CAD Model

1.2 Design Boundary condition for Hood

• Its opening angle, the opening angle of a car varies region to region. Because the average height of Indian is 5.5feet, European average height is 6feet.

Fig: Design Boundary Condition

2. Components of the Hood

1. Inner Panel
2. Outer Panel
3. Reinforcements
4. Embosses
5. Hood Support (Gas Stay, Support Rod)

Hood Inner Panel: Inner Panel is the major part which acts as support material for outer panel. It consists of embosses which helps in distribution of forces during the impact. Inner panel is offset of outer panel from the given data. The thickness of the inner panel is 0.75mm as mentioned.

Fig: Hood Inner Panel

Hood Outer Panel: Outer panel is the extracted model from prototype design. The skin of the inner panel is outer panel. It gives the luxurious look to the car. Through hem the outer panel is joined to the inner panel. The relief is given at the corners. Reliefs are provided on the surfaces to avoid springback situations.

Fig: Hood Outer Panel

Reinforcements: Whenever we add weight to a material there is a loss of strength on that area locally, to compensate the loss reinforcements are added.

Fig : Latch and Hinge Reinforcement

Embosses: Embosses will provide the strength to the panel. These will help in the distributing the forces at the outside, hence the direct impact will not be on the passengers. The emboss depth is kept at maximum 5mm.

Hood Support: Hood support has two types 1. Hood Stay 2. Gas Stay

1. Hood Stay: A hood stay is an apparatus for an engine room of a car, which can safely keep an engine hood in an open state even if an external force is abruptly generated due to vibration, wind and can facilitate an opening or closing operation of the engine hood. Gas stay of support rod will help in controlling the opening angle. By predefining the length of the rod we can vary the distance of the hood. Rod is nor straight is will be having some bends. Because these gives the strength to the parts. We can give any curvature to the support rod to improve the strength. But the curvature shouldn’t be more than 35mm. We can give any curvature to the support rod to improve the strength. But the curvature shouldn’t be more than 35mm.

Fig: hood Stay / Support Rod

2. Gas Stay: Gas stay of support rod will help in controlling the opening angle. By predefining the length of the rod we can vary the distance of the hood. Stud balls are used to fix the gas stay. Stud balls are used to fix the gas stay.

Fig: Gas Stay

Stiffener pad: Added to avoid vibration when in motion.

Mastic seal: Mastic sealants are hard rubber kind of materials which are placed in between the inner panel and outer panel. Theses oozes out and help in holding the outer and inner panel together. Every mastic seal has a tendency to improve the strength locally at 80mm.

Fig: Mastic Seal

Wrap around hood:

1. Inline Hood: The end point of the car lies on the fender
2. Wrap around Hood: The end point of the car lies on the hood.

Side reference line: from the ground when we take a 45-degree angle and when it touches end point of the car is side reference line.

Wrap around Hood: from the ground when we take a 45-degree angle and when it touches end point of the hood is wrap around hood.

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

Fig: Hem

Position of 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 flanges are positioned at their respective positions. Then the line is drawn at a straight. Now the trajectory is derived from the hinge axis and the center distance from the striker. It is denoted using the circle.

Fig: Position of striker

Hood head zone for Lock striker: The hood is designed to open at an angle based on the average height of the people in that region / country.

Euro – Ncap

The European new car assessment programme. They are the team who analyses and give rating on hoe safe is the car.

Fig: Impact Zones

HIC Criteria:

=<1000(Green) Better Zone

1000 to 3500 (Yellow)

>3500 (Red)

Front View:

Back View:

Top View:

Bottom View:

https://drive.google.com/file/d/14lf-_0CcXZmgVPWPseRPaTu4R_zx6RxA/view?usp=sharing

Conclusion:

Hood is designed in NX Cad tool with undestanding the design requirements, and considering the passangers and pedestrians safety.