Page 553 - Automotive Engineering Powertrain Chassis System and Vehicle Body

CHAP TER 1 6. 2 Standard sedan (saloon) – baseline load paths

Moment equation Equations (16.2.48)–(16.2.54) are seven simulta-
0
0
0
2 0:5
0
2
Q ðl þðh 3 h 1 Þ Þ Q w ¼ 0 (16.2.49) neous equations with seven unknowns Q 1 ... Q 7 , so their
1 6
3
solutions can be obtained by standard mathematical
16.2.4.2.13 Roof (8) methods. Equation (16.2.54) can be simplified by taking
moments about the lower corner of the windscreen
This again is in complementary shear. pillar. This will eliminate terms in Q 2 ,Q 3 and P 7 but
0
0
0
Moment equation the numerical solutions will be unchanged. These equa-
tions provide the values of all the forces on the SSSs of
0
0
Q l 7 Q w ¼ 0 (16.2.50) the ‘torsion box’. When evaluating these forces acci-
4
1
dental errors may occur, therefore it is imperative that
the sideframe equilibrium is verified. This is done by
16.2.4.2.14 Backlight frame (16) resolving forces vertically and horizontally using the
Once again this is in complementary shear. following equations:
Resolve forces vertically
Moment equation
0
0
0
0
0
0
Q Q cos q 1 þ Q cos q þ Q P P ¼ 0
2
1
3
2
6
2
5
2 0:5
0
2
0
Q ðl þðh 3 h 2 Þ Þ Q w ¼ 0 (16.2.51) (16.2.55)
1 8
5
Resolve forces horizontally
16.2.4.2.15 Panel behind the rear seats (9)
0
0
0
0
0
0
2
Loads P 8 applied from the rear quarter panels apply a P P 0 12 þ Q Q sin q 1 Q Q sin q ¼ 0
3
7
5
4
7
0
moment to this panel. Edge load Q 1 is applied to the top (16.2.56)
edge from the backlight frame, therefore an equal and op- Provided these equations are satisfied, the correct
0
posite force Q 1 acts at the lower edge. All these forces apply force conditions through the structure have been
moments in the same sense, therefore to maintain equilib- determined.
0
rium Q 6 at each side must act in the directions shown. It should be observed that lateral loads cause addi-
Moment equation tional bending on the front inner wing panels, rear
quarter panels, parcel shelves and shear on the dash
0
0
0
Q w Q h 2 P t r ¼ 0 (16.2.52) panel, windscreen frame, roof, backlight frame, and seat
6
1
8
panel. The main floor and the sideframes have both ad-
16.2.4.2.16 Floor panel (11) ditional shear and bending. These additional loads must
There are a large number of loads acting on this SSS. be added by superposition to those obtained in section
Shear loads, tension/compression loads and moments act 16.2.2.
on the front and rear edges plus shear loads from the
front and rear transverse floor beams. In order to achieve 16.2.5 Braking (longitudinal) loads
0
equilibrium, loads Q 7 are required at the sides.
Moments about the centre of the floor (O F ) A passenger car subject to braking conditions has addi-
0
0
0
0
0
0
ð2P Q Þl 5 =2þP t þ2M ð2P þQ Þl 5 =2 2M 0 tional loads shown in Fig. 16.2-29 over the normal
20 1 5 f 1 21 1 2 bending loads. The proportion of the total braking force
0
0
P t r þP 16 ðl 3 l 5 =2ÞþP 17 ðl l 5 =2ÞþQ w ¼ 0
10 4 7 applied at the front wheels is usually in the order of 50 to
(16.2.53) 80%. This is due to the design of the braking system and
because additional vertical load R ZXF is applied to the
16.2.4.2.17 Left-hand sideframe (12) front wheels. Modern braking systems may have variable
The forces acting on this SSS are shown (Fig. 16.2-28). brake proportioning to suit the decelerating condition.
These are the equal and opposite reactions to the loads For this analysis the assumed proportion of braking on
on the previous six SSSs plus loads from the front and the front axle is:
rear parcel shelves and from the transverse floor beams.
R XF
Moments about the centre of the sideframe (O S ) n ¼ (16.2.57)
R XF þ R XR
0
0
0
Q l 5 =2 þ P ðl 3 l 5 =2Þþ P ðl l 5 =2Þ Q 6 l 5 =2Þ
2 1 2 4 Forces R XF and R XR are applied at the front and
0
0
þP ðh 1 h 3 =2Þ P ðh 2 h 3 =2Þ Q h 3 =2 rear tyre to ground contacts which are h f below the
4
12
7
0 0 base of the structure. The load transfer onto the front
Q 7 h 3 =2 Q ðh 3 =2Þ sin q 1 Q ðl 5 =2 l 6 Þ cos q 1 axle and off the rear axle is obtained by taking mo-
3
3
0
0
Q ðh 3 =2Þ sin q Q ðl 7 þ l 6 l 5 =2Þ cos q ¼ 0 ments about the rear tyre/ground contact point (see
2
2
5
5
(16.2.54) Fig. 16.2-30):
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