Automobile in very EASY WAY by ANUBHAV SINGH

1. MEE 7101
AUTOMOBILE ENGINEERING
Prepared by: Deepak Sharma (Asst. Prof.)
Department of Mechanical Engineering
IET, GLA University Mathura
Lecture: 2
Types of resistance in automobiles

2. Types of Resistance in Automobile
This is the resistance a vehicle faces
while attempting to move from a stall condition
or
while accelerating.

3.  This resistance must be overcome by the power
plant of the automobile in order to sustain
motion.
 When the power produced is smaller than the
resistance to motion, the vehicle will gradually
slow down.
Types of Resistance in Automobile

4. In case of bicycle:
1. We must have experienced the slowing down of
bicycles if we stop pedalling.
2. The bicycle also slows down if we go uphill.
3. The bicycle also slows down if wind blows from
front.
4. A poorly inflated tire also causes the bicycle to
slow down.
5. These are the resistances that force the vehicle to
slow down under their effect.
Types of Resistance in Automobile

5. Broadly the resistances can be categorized into the
following categories:
• Aerodynamic drag
• Gradient resistance
• Rolling resistance
• Inertia
All the above produce a restraining force working against
the tractive force.
Types of Resistance in Automobile

6. The tractive force must be greater than or
equal to the resistive forces in order to
maintain a sustainable motion.
We can balance them as,
F = F req = FA + FG + FR + FI
Types of Resistance in Automobile

7. Where;
FA= Force due to air resistance,
FG=Force due to gradient of a slope,
FG = Force due to rolling resistance,
FI = Force due to moving or static inertia.
Types of Resistance in Automobile

8. • The last one FI comes into the picture only
when the vehicle accelerates or decelerates,
while the first three always offer a resistance
even when the vehicle is moving at a constant
speed.
Types of Resistance in Automobile

9. Air resistance /Aerodynamic drag FA
When a body travels within a dense medium,
the molecules of the medium collide with the
moving object and thereby absorb some of the
energy.
This is felt as a resistance to the moving object.

10. 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%)
Air resistance /Aerodynamic drag FA

11. It increases proportionally with respect to,
Density of medium.
 velocity of automobile.
Air resistance /Aerodynamic drag FA

12. Mathematically it can be expressed as
FA = −½ × Cd × P × V²
• Cd = Coefficient of drag
• P = Pressure
• V = Velocity of the vehicle
Air resistance /Aerodynamic drag FA

13. Gradient resistance:FG
When the vehicle travels uphill, a component
of its weight works in a direction opposite to
its motion.
If some energy is not supplied to overcome
this backward force, then the vehicle would
slow down, stall and roll backwards.

14. Gradient Resistance:FG
The gradient resistance is given by:
FG = WSin θ

15. When a vehicle rolls, it rolls with its tires in
contact with the road surface.
The relative motion of two hard surfaces
produces a friction. Further, neither the road,
nor the tire are perfectly rigid.
Hence, both flex under the load slightly.
Rolling resistance FR

16. • As there is a gradual deformation at the contact
between the road and the tire,
• greatest at the bottom most point and least at
the entry and exit points,
• the slip of the tyre with respect to the road
produces another type of loss of energy which
results in a resistance.
Rolling resistance FR

17. Rolling resistance FR
Composed primarily of
1. Resistance from tyre deformation (90%)
2. Tyre penetration and surface compression ( 4%)
3. Tyre slippage and air circulation around wheel ( 6%)
4. Wide range of factors affect total rolling resistance

18. Rolling resistance is composed of the following
components:
• Tyre Rolling resistance: FR,T
• Road rolling resistance: FR,Tr
• Resistance due to tyre slip angle: FR,α
• Resistance due to bearing friction and residual braking:
FR,fr
Rolling resistance FR

19. Hence the rolling resistance offered may be
written as:
FR = FR,T + FR,Tr + FR,α + FR,fr
Rolling resistance FR

20. Tractive force
The term tractive force can either refer to the
total traction a vehicle exerts on a surface,
or
The amount of the total traction that is parallel
to the direction of motion.

21. Tractive effort
• Is the force generated by a vehicle's engine or
motor in order to
generate motion through tractive force.
Tractive effort differs from tractive force,
which is the actual force applied at the road
surface, by the amount of rolling
resistance present. In mathematical terms,
• Tractive effort = tractive force + rolling
resistance

22. Gradeability of a vehicle
Gradeability is defined as the grade angle that the
vehicle can negotiate at a certain constant speed.
For heavy commercial vehicles the gradeability is
usually defined as the maximum grade angle that
the vehicle can overcome in the whole speed
range.

23. A
B C

24. Total Resistance