Design of backdoor
Aim : To design Backdoor/ of a car and to locate the latch, striker & hinge position in the backdoor for smooth operation.
Explanation :
Backdoor / Rear door / Tailgate / Trunk
We need to open, close and lock the trunk. When we need to access this storage space our hands are often full of something, whether groceries, tools, sports equipment or children. Sometimes we may want to open the trunk while inside the car, in the driver’s seat. In the past, all these functions were performed manually and were all based upon mechanical systems. This is changing, and like many vehicle subsystems, the trunk has electronic assistance using electric motors controlled by networked microcontrollers, following the digitalization and electrification trends that are transforming the car.
Fig.1.1.
Types of Backdoor
1) Gas stay type (Gas springs / Gas dampers)
2) Power spindle type
Have you ever tried lifting the tailgate of your car with just one finger? How come you can lift a heavy piece of metal and glass with so little force? The answer, if you didn't know already, lies in those clever piston-like hinges that support the lid either side. They're called gas springs and they make our lives a whole lot easier in all sorts of ways.
Suppose there were no springs on the trunk lid of your car. It would be really heavy to lift, for one thing. There'd be nothing to hold it up in the air when you wanted to load in your shopping, which would be a real nuisance. With the lid opened up fully, the spring would be stretched out so much that it would pull straight back down again!
How does a Gas stay works ?
Gif.1.1.
A gas spring is a bit like a super-sturdy version of a bicycle pump, only it's filled with pressurized nitrogen gas (the major constituent of the air around us) and oil and completely sealed up so they can't escape. The gas allows the spring to store energy, while the oil damps (slows and smooths) the movement of the piston and also provides lubrication. Just like in a bicycle pump, there's a tight-fitting piston mounted on a rod that can slide back and forth inside a cylinder (made from heavy gauge steel not light plastic as in a bicycle pump).
Push on a gas spring and you force the piston rod and piston into the cylinder (Opening of the Backdoor) and this compresses the gas. Stop pressing and let go and the pressure of the gas pushes the piston back out again (Closing of the Backdoor)
Fig.1.2. Gas stay
The power spindle drive is capable of opening and closing even large and heavy tailgates. Depending on the tailgate’s weight, kinematics and supporting mechanism, one or two drives can be installed.
Fig.1.3. Power spindle Type using motor(A) & Gear(B)
Design of Backdoor
Backdoor consists of inner panel and outer panel just like Hood. The inner panel is designed as per the outer panel design which is given by the styling team.
Backdoor Outer
Fig.1.4.
Backdoor Inner
Fig.1.5.
Backdoor Inner panel features
1) Embosses
2) Reinforcements
3) Latch & striker & Hinge Positions
4) Gas stay position
5) Hemming of outer panel with inner panel
Embosses - The implemet of embosses are very important on the inner hood since it plays a important role in saving human life during a crash from the back. The embosses are designed in Y & V direction so that during the crash the forces disspiates outwards as shown in Fig.1.6. This will reduce the impact on the passengers in the back.
Fig.1.6. Forces dissipated outwards in a backdoor due to embosses
The other cutout regions present in the backdoor has its own importance. cutouts have been made to accomodate wiper motor assembly, latch and striker motor, and to maintain the C.G of the backdoor to ensure easy handling of the backdoor.
Fig.1.7.
Reinforcements - In backdoor to accomodate Latch and striker, Hinges & Gas stay we have to remove some material which will result in loss of strength of the material locally. Hence to improve strength locally we provide these reinforcements. The reinforcements provided in the latch and striker area is called Latch and Striker Reinforcements & the reinforcements provided in the Hinge area is called Hinge Reinforcements and reinforcements provided in the Gas stay region is called Gas stay reinforcements.
Fig.1.8.
The embosses are provided in the reinforcements to avoid the tearing of the parts. Diabolo embosses are provided both in reinforcement & in the inner panel body at the curved surfaces.
Fig.1.9 Diabolo Emboss
Latch & striker & Hinge Positions
For the proper opening & closing of the backdoor, the striker should be perpendicular to the trajectory of the backdoor. Firstly the hinge is positioned and an axis is drawn as shown in the fig.2.0. The Trajectory is derived from the hinge axis and the centre distance from the striker. It is denoted as a circle as shown in fig.2.0.
Fig.2.0.
Fig.2.1. Striker is perpendicular to the Trajectory
Hinge
Fig.2.2.
Latch & Striker
Fig.2.3.
Gas stay Position
The Gas stay positioning is very crucial for smooth operation of the backdoor. Its position depends on the types of gas stay, weight of the door and other features.
The standard criteria that are followed is that the gas stay should be positioned in such a way that its distance from the hinge should be <90 mm & > 60 mm and the angle of the gas stay wrt the hinge should be between 80 degrees - 90 degrees.
Hemming
The Hemming is a process where the outer panel is joined with the inner panel of the backdoor by adding extra material on the outer panel and made to wrap around the inner panel as shown in the Fig.2.4. This wrapping is done by running the ball rollers throughout the ends of the outer sheet.
The Hemming is done to avoid spot welds. After Hemming, sealents are provided to achieve the water tightness.
Fig.2.4.
Conclusion
The Backdoor of the car is designed by using appropriate design methodologies, and provided with necessary reinforcements & embosses
To view the model in Nx Ca, Please go to the link below :
https://drive.google.com/file/d/1hNbHI8f2lyj7rEeruIFXYkDJiIygl6tX/view?usp=sharing