Quote:
Originally Posted by 1100D For space-frame buses, (or modular coaches) its (the upward customization) not done so easily without factoring in load calculations which I dont think the normal indian bus body builders can do. |
What on earth is a space-frame bus? Haven't heard of any such thing.
Is it a good time for a body-engineering. discussion?
Here goes...
Ladder chassis.
World's earliest kind of chassis.
Basically two longitudinal rails joined by multiple lateral and crossed braces.
The rails take up acceleration and deceleration forces.
Lat braces provide torsional firmness and take the cornering and lateral yaw loads. Naturally, the "Z" dimension is weakest. (as in: vertical loading, speed-breakers and potholes).
Backbone
For small sports cars, there's the fibreglass body on a rigid steel tubular backbone. This is used in the Lotus Esprit. Also Fibreglass body on a lattice TSF backbone. This is used in the TVR.
Steel, ULSAB and carbon-fiber monocoques
Steel monocoque (aka integral body or unibody) is a one piece integrated chassis-body.
99% vehicles use it. Copiously uses metal, so you can build-in crumple-zones.
Hopelessly heavy. Only makes sense when you can afford a huge factory with
facilities for huge stampers, expensive moulders and welding robot assembly lines.
ULSAB (Ultra Light Steel Auto Body) monocoque
ULSAB uses steel too thin for the steel-monocoque stamping presses.
Basically a thin steel tube is placed in a shaping die.
Then very-high pressure (300 - 1500 bar) hydraulic fluid is pumped into the tube.
The fluid expands the tube to assume the inner surface of the die.
This is called
hydroforming.
Uniform fluid pressure gives uniform steel thickness, unlike the earlier stampings.
Panels for ULSAB usually use
sandwich steel -- two very thin steel skins with a sandwiched polypropylene core. This yields excellent rigidity and very low weight. But you cannot use welding. You will melt the polypropylene sandwich. Panels must be riveted or adhesive-bonded.
For doors, hoods, deck lids and hatchbacks, there's the
ULSAC (Ultra Light Steel Auto Closure). Yields door structures that are 46% lighter than average frameless doors.
Invented in 1998, ULSAB will eventually replace conventional monocoque. Meets tough structural and crash criteria while weighing 25% less than steel monocoque. Used in BMW 3-Series.
Carbon-fibre monocoque
The name is self-explanatory.
The world's first carbon fibre monocoque bus was the 1988 Neoplan Metroliner. This is a city bus, with a small diesel engine on the roof that charged batteries under the floor, that powered the bus using electric motors.
Let's come to Space Frame construction.
Steel and Alloy space-frames
Steel space-frame
The 3d tubular-steel space-frame has much better strength than the ladder chassis.
circular sections provide max. strength.
Square sections easy to put the body panels on.
Weak areas are the door sills.
These must be high to take the bending stresses.
So no choice but to use Longitudinally hinged doors (aka Gullwings)
or Horizontally hinged doors (like the Countach).
Alloy space-frame (ASF)
The material used is high-strength aluminium alloy.
With this material you construct
the components of the space-frame, viz.:
- aluminium extrusions
- pressure die-cast nodes
- aluminium sheet stampings
At the corners, where extrusion meets extrusion, you use the pressure die-cast nodes. These take the stresses. Everything is bonded together by laser welds.
This is very space efficient yet lighter than steel monocoque.
Audi A8 was the world's first mass produced ASF-chassis car.
...end of my body-engg. gyaan.
The Volvo B7R is a simple ladder chassis -- world's earliest form of automotive construction.
Ram