Hood design-Week 2
CAR HOOD DESIGN
AIM: To design a car hood and understand the mechanism behind the design of hood, the development of hood &its safety feature as per the design consideration.
The following tasks are performed:
- Design outer panel with hem
- Develop the inner panel
- Develop all necessary reinforcement
- Mirror and position hinge and striker
- Provide mastic data
- Provide required emboss definition
- Develop a detailed report for mastic position and Emboss you have placed
MASTER SKETCH:
DATA TO BE USED:
- Outer Panel Thickness = 0.75mm
- Inner Panel Thickness = 0.75mm
- Reinforcement Thickness = 1.5mm
HOOD:
A car hood, also referred to as a bonnet in some other countries, is the hinged cover that rests over the engine of a front-engine vehicle. Its purpose is to provide access to the engine for repair and maintenance. A concealed latch is typically used to hold down the hood. On vehicles with an aftermarket hood and on racecars, hood pins may be used to hold down the car hood. Hoods sometimes also contain a hood scoop, wiper jets, power bulge, and/or hood ornament. Car hoods are typically constructed from steel and sometimes from aluminum. Aftermarket car hoods may be constructed from various other materials, including carbon fiber, fiberglass, or dry carbon. The hood design may vary from one make and model to another, including SUV.
Concerns regarding the severity of a potential pedestrian head injury during a collision with a motor vehicle have led to advanced hood designs on many models. Such designs may include a multi-cone inner hood panel design. An active structure that is capable of pushing the surface of the hood away from the vehicle's hard motor components in the event of a pedestrian crash is also in use. Pyrotechnic or spring force designs are often used in active-hood design.
PARTS OF AN HOOD:
Basically the hood has the inner panel, outer panel and reinforcement and emboss.
Latch and striker mechanisms s used to open and close the hood whenever needed
There are two types of hood support:
- Gas stay
- Support rod
GAS STAY:
Spring stays are designed to be used on upward lifting doors, once you have opened the doors slightly the spring will push the door to the fully open position, Euro fit stock various size springs depending on the door size requirement.
This is mostly used for where the car bonnet weight is heavy.
SUPPORT ROD:
This is widely used in many cars because this is very easy and cheap. In this type we have to lift the hood and place the support rod in the space provided either in hood or engine compartment. This is mostly used for where the car bonnet is light in weight.
INNER PANEL:
Inner panel supports outer panel. It consist of different embosses and hole at different places. Embosses provide stiffness as well as dissipate energy towards hinges. To determined the most effective position of hole, the method of modal stiffness is employed. Inner panel is offset of the parent work surface. Inner panel thickness is 0.75mm.
EMBOSS:
The geometry is created based on the master section that was designed above. After performing the initial stages of design, we will provide local embosses to strengthen the component. The component will be strengthened based on the master section. When a force impacts the hood from the front, it travels in an upward direction. The component is designed to divert the force away from the passengers into the hinges, as shown in the image below. The embosses in the inner panel are made according to the diversion of the load path. The emboss depth is kept at a maximum of 5mm to be on the safer side so that the part is manufacturable.
To provide strenth to the inner pannel and to distribute the force produced during the impact with pedstrian or other obstacles to ensure the saftey of the passengers.The forces are directed outwards through the embossing path.
OUTER PANEL:
Outer panel is nothing but a outer skin of inner panel. Otherwise called as a cover of inner panel. It is the part, which gives luxurious look to the hood or bonnet. Outer panel and inner panel cannot join by any welding process like spot welding or rivet, which spoil the outer look of a car. The outer panel is generally extracted model from the prototype design.
Mastic Sealant:
The Mastic sealant or the Mastic point is an elastic compound that behaves like a rubber. The mastic points are defined on the hood inner panel where the hood can easily deform. They help the hood outer panel to come back to its original shape after it gets deformed. The mastic has an influence area of 80mm.
HEMMING:
Hemming is the process of joining both the outer and inner panel together. The hemming process roles and wraps the hood outer panel around the inner panel and holds it tightly together. The following are the dimensions followed for hemming.
HEMMING DATA:
POSITION OF HINGE AND STRIKER:
For positioning hinge and striker, we have to place hinge tentitively and take hing axis point and place position from data taken from the parent car or our own. The other major functional of the hood is the opening and closing of the hood. This is done with the help of the latch and striker. To position the latch and striker effectively, we position the hinge and draw the hinge axis. Now, using the hinge axis as the centre we draw a big circle to the position where we need the latch to be placed. Then, we draw a tangent line to the circle at that point and place the latch in that region.
Building re-enforcements and crash bead:
After the development of the entire inner panel for the hood, we need to develop some additional necessary re enforcements. The Latch striker and the hinges will need a re-enforcement that needs to be developed. All the re- enforcements are made from sheet metal of thickness 1.2mm.
The reinforcements are attached to the hood inner panel using spot welding method. The positions to be spot welded are provided by the design team.
ASSEMBLED VIEW OF HOOD:
CONCLUSION:
All the parts of the hood are designed based on the required condtions& given values and assembled togather to complete the hood design.