Chapter 2 _1_ - Vehicle Dynamics Basic Principles of Road...

Vehicle Dynamics:
Basic Principles of Road Vehicle
Interaction and Performance

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Why we learn this?
head2right Safety
head2right Highway design (sight distance, stopping distance,
lane widths, vertical/horizontal curves, grades,
speed limits)
head2right Traffic analysis (flow capacity, delay, traffic signal
timing)
head2right Fuel economy

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What are involved?
head2right Vehicle performance
head2right Straight-line performance (Accl/decl/max_v/grades)
head2right Corner performance
head2right Tractive Effort (engine-generated)
head2right Resistance
square4 Aerodynamic
square4 Rolling
square4 Grade (Gravitational Resistance)

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Tractive Effort and Resistance
Moving direction
A Four-Wheel Drive Vehicle with acceleration a on flat road

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Resistance is defined as the force impeding
vehicle motion
1.
Aerodynamic resistance: R
a
2.
Rolling resistance: R
rl
3.
Grade resistance: R
g
If F denotes tractive force, then
Where was R
g
on last slide?
Tractive Effort and Resistance

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Tractive Effort and Resistance
On a slope with angle θ
g

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Aerodynamic Resistance R
a
(lb|N)
Composed of:
1.
Turbulent air flow around vehicle body (85%)
2.
Friction of air over vehicle body (12%)
3.
Vehicle component resistance, from radiators
and air vents (3%)
2
2
V A C R
f D a
ρ
=
from National Research Council Canada
What are C
D
, A
f
, and V?
A
f
: Frontal area of the vehicle

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Aerodynamic Resistance:
Air density
The dry air density gradient in mid-latitudes
Source: http://www.auf.asn.au/meteorology/section1a.html

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Aerodynamic Resistance: drag coefficient
C
D
(unitless)

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Aerodynamic Resistance: drag coefficient
C
D
(unitless)

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Guess your Drag Coe.