Transcript ALTERNATIVE CONSTRUCTION FOR BODY SUBASSEMBLIES …

ALTERNATIVE CONSTRUCTION FOR
BODY SUBASSEMBLIES AND MODEL
VARIANTS
INTRODUCTION
Variations from the basic ‘standard sedan’ structure  2
levels:
Body subassemblies
Major subassemblies can take many different forms such as
suspension mountings and passenger compartment
Vehicle model variants
Vehicle model may be produced in a range of variants
E.g.: station wagon, hatchback, convertible, pick-up truck, etc.
Structural features are significantly different from sedan
ALTERNATIVE CONSTRUCTION FOR MAJOR
BODY SUBUNITS
In standard sedan:
Suspension loads (RF & RR)
Carried by the end structures
i.e. inner fender assemblies
Shear panel reactions
Carried by the front or rear
compartment bulkhead
Flange reactions
Taken by parcel shelves and floor
In this lecture:
Alternative end structures at front & rear are considered
Variations are based on the standard sedan
All discussions are in relation to the EXPLANATIONS OF TORSION
AND BENDING LOAD CASES on the standard sedan
It is essential to configure the structure correctly.
If not, local deficiencies might happen
This will lead to serious degradation of overall structure
Rear Structures
– Rear
Suspension Supported on Floor Beam
Normally for trailing arm & similar rear suspensions
Floor beams:
Q8  RR L2 L1  L2 
Q9  RR L1 L1  L2 
Rear valance :
Q10  Q9 S R B
Sideframes:
QX 2  Q10 L1  L2  h2
Load applied to the compartment
•Q10, Q6, fig. 5.12
•Pass compartment
•Bending, Q8, Q9
Rear Structures
– Suspension Towers at Rear
For strut type rear
suspension
Need rear suspension
towers
If it is closely built into the
sideframe, hence Fig. 6.3
• line of action of strut, couple, torsion
• vslc: brace
• tlc: brace has same direction, stiff in shear add structure  assgmnt
Frontal Structures
– Grillage Type Frontal Structure
For front suspension that is attached to the lower engine rails
T  RF S F
RF  P4  P1  0
Momentabout H :
RF L1  P4 L2
 P4  RF
L1
L
 1 T
L2 S F L2
 L   L T
P1  RF 1  1   1  1 
 L2   L2  S F
P1  RF
P4 S F  P3 B
 P3  P4
SF
L
 1 T
B L2 B
Assgnmnt
Frontal Structures
– Grillage Type Frontal Structure With Torque Tubes
P1   RF
M 1   RF L1
Missing or Flexible Shear Web in Inner Fender
Missing Shear Web in Inner Fender:
Upper Rail Direct to A-pillar
R1  RF b a  b 
RF  R1  R2
R2  RF a a  b 
CLOSED INTEGRAL STRUCTURES
Different closed body configurations mounted on a common
floor pan assembly will be discussed
Standard sedan floor is often used for:
Estate car
Hatchback
Rear structure experienced a little change
Extended for estate car
Shortened for hatchback
Bending load case can be treated in the same way as before
Rear door frame for estate car will function in a similar way to the
rear panel in standard sedan
The sill of the rear door will:
Carry bending & shear loads
Transfer forces to the sideframe
Torsion load case must be
treated differently than the
standard sedan
Special care must be taken
when analyzing the rear frame
for estate/hatchback
Estate Car/Station Wagon
Modern station wagon has a rear door that is near vertical &
constructed in a single or near single plane
Can be treated as single SSS
Primary structural function in torsion case is to transfer shear from
the roof panel to the floor
Hatchback
This style of body has caused particular structural problems
To minimize drag, hatchback rear frames are constructed with a
sloping backlight with a short horizontal surface at waist
height & a vertical surface between waist and rear bumper
No longer a plane structure but 3 planes
Structural function remains the same as estate car
i.e. to transfer shear from roof to floor during torsion
Q1a  Q2 w  0
Q1c  Q3w  0
2M z  Q1b / 2
PRU w  2 M R  0
PRLX w  2 M Z  0
PRLZ w  2 M X  0
OPEN VEHICLE: bending load case
The sidewalls are the major members
carrying bending moment.Thus it needs
extra care to stiffen the structure
All edge loads are well supported by
the components
OPEN VEHICLE: torsion load case
The open car suffers in the torsion case due to not having a closed box.
This creates out-of-plane forces to the floor and thus breaks down the SSS
Torsion stiffening measures:
1. Adding in a torsionally stiff grillage
a) Cruciform braced members in the floor
b) Tubular backbone members
c) Full underfloor grillage structure
2. Adding in torsion box-type members at the following areas:
a) luggage or engine compartments
b) region of engine bulkhead, parcel shelf and lower A-pillar
c) region under the rear seat or near fuel tank