Hood design-Week 2

Introduction to 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. Car hoods are typically constructed from steel and sometimes from aluminum.

Hoods are usually made from the same material as the rest of the body. This can be steel, aluminum, fiberglass, or carbon fiber. However, some aftermarket companies produce fiberglass or carbon fiber steel hood replacements to make the vehicle lighter.

The hood release system is common on most vehicles and typically consists of an inner hood latch/lock handle, a hood release cable, and a hood lock assembly. The hood lock handle is usually located under the steering wheel, next to the driver’s seat, or in the door frame.

For racing cars or vehicles with aftermarket hoods (that do not use the factory latch system) the hood can be held down by hood pins. Some aftermarket hoods that have a latch system still have hood pins to keep the hood buttoned down if the latch fails

Design Considerations for HOOD

• Pedestrain safety
• Occupant safety
• Opening angle of Hood
• Wrap around distance(WAD)
• NVH ( Noice, Vibration, Harness)
• Styling
• Ease in Manufacturing

The 1st and most important safety requirement to be considered while designing the Bonnet is the frontal collision requirements.

In this image, you can see the deformation on a hood that underwent a frontal collision:

It is clear that the design intention of the hood according to the frontal collision requirement is that the hood crushes and dissipates forces in the upward direction and to the hard points on the hood thereby deflecting the force on to the body and not the passengers.

Regarding the safety of the pedestrians, the above image from Euro NCAP shows the area of impact for a child and an adult. It is of utmost importance that we make sure not to place re-enforcement on the areas prone to high head impact. Also, the child impact area is designed with lesser thickness than the adult impact area so that in the event of a frontal collision where a child is involved, the bonnet will absorb the impact of the crash and crumble to protect the child’s head from absorbing the force.

Parts in HOOD

1. Hood outer panel
2. Hood inner panel
3. Latch and Striker
4. Hinge Assembly

Hood Inner panel

In the inner panel only we can research and implement triage safety of pedestrians and as well as the driver. In this panel only we can attach the reinforcement embossed mastic points etc.

It as an object of the present invention to provide a hood inner panel capable of reduction of reaction of force of the hood inner panel even if a level of deformation of a hood of vehicles increases and ensuring a sufficient energy absorption capacity

Hood outer panel

It provides aesthetic look for hood of the car design styling team provide skin for outer panel shape size position should be according to safety norms while designing pedestrian safety is considered NY hemming process the outer panel is made to attach with inner panel mastic sealants are provided between outer panel and inner panel to reduce vibration

Latch and Striker

The main function of this part is to lock the hood at an angle with the help of support rod or gas stay for insepection and performing services. Latch is a kind of fixing member which is used to fix the hood and striker is the part which will be having Hook in wich support rod is placed

Hinge Assembly

a pair of hoinges are required to open and close the hood , there hionges are placed on the hood inner panel at either sides this hing assembly should play a critical role for opening angle and placement ofd striker on the hood inner panel

Opening and closing angle of Hood procedure

The opening angle is dependent on regions like every country will be having their own opening angles depending on the height of the human in that country

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 center 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.

Modelling of Hood and its Features

Geometry and emboss creation:

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:

Fine-tuning the emboss:

To make the component easy to manufacture, all the sharp corners from the embosses are removed. The curvature intersections from different nearby embosses are blended out to produce a smooth transition.

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.

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.

After the hemming process is done, now we need to provide corner relief on the corners of the hood so that the part is manufactural

Points to be considered while medelling Hood inner panel

1. Minimum fillet radius = 3mm+Thickness
2. No sharp corners inside the component
3. No curvatures lesser than 5mm
4. Mounting areas and welding areas need to be flat
5. Provide appropriate corner relief on the area of curvature.

Given Data

1. Hood outer styling surface
2. Master section of hood inner panel
3. Hinge assembly
4. Striker
5. Thickness of hood inner and outer panel is 0.75mm
6. Reinforcement thickness 1.5mm

Conclusion :

Hood Assembly have been Model by using NX CAD software version 12 under the regulations of the manufacturer standard