SHRI SHIVAJI INSTITUTE OF ENGINEERING AND

MANAGEMENT STUDIES, PARBHANI

BTAPE504D
Automobile Engineering

Lecture Notes

BY

PROF. PRAMOD A. SADAVARTE

DEPARTMENT OF MECHANICAL ENGINEERING

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 BTAPE504D PEC2 Automobile 3-0-0 3 Credits
Engineering

Course Objective:
The objective of this Course is to provide the Basic Knowledge of Automobile
Engineering which useful for a student in preparing for an Automobile
Engineering career.

Course Outcomes (CO):

After completion of this course, students will be able to:

CO1. Identify the different parts of the automobile.

CO2. Explain the working of various parts like engine, transmission, clutch,
brakes etc.

CO3. Demonstrate various types of drive systems; front and rear wheels, two and
four wheel drive.

CO4. Apply vehicle troubleshooting and maintenance procedures.

CO5. Analyze the environmental implications of automobile emissions. And

suggest suitable regulatory modifications.

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S. S. I. E. M. S. PARBHANI UNIT II Steering and Suspension Systems

Unit2: Steering and Suspension Systems

Steering system;
Principle of steering,
Centre point steering,
Steering linkages,
Steering geometry and wheel alignment,
Power steering.

Suspension system:
Its need and types,
Independent suspension,
Coil and leaf springs,
Suspension systems for multi-axle vehicles,
Troubleshooting and remedies.

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S. S. I. E. M. S. PARBHANI UNIT II Steering and Suspension Systems

Steering System
• Steering provides the directional change for the movement of the
automobile and it maintain in a position as per the direction of the
driver‘s decision without strain on him.
• Steering is done by the movement of the axis of rotation of the front
wheel with respect to chassis frame.
Requirements of Steering System:
a. It must keep the wheel at all times in to rolling motion without rubbing on the road.
b. This system should associate to control the speed.
c. It must light and stable.
d. It should also absorb the road shocks.
e. It must easily be operated with less maintenance.
f. It should have self-centering action to some extent.

Layout of Steering system

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The fundamental problem in steering is to enable the vehicle to traverse an arc such that all four wheels
travel about the identical center point. In the days of horse-drawn carriages, this was accomplished with
the fifth-wheel system depicted in Fig. 7.1.
Although this system worked well for carriages, it soon proved unsuitable for automobiles. In
addition to the high forces required of the driver to rotate the entire front axle, the system
proved unstable, especially as vehicle speeds increased. The solution to this problem was
developed by a German engineer named Lankensperger in 18 17. Lankensperger had an
inherent distrust of the German government, so he hired an agent in England to patent his idea.
His chosen agent was a lawyer named Rudolph Ackerman. The lawyer secured the patent, but
the system became known as the Ackerman system.
Figure 7.2 depicts the key features of this system. The end of each axle has a spindle that pivots
around a kingpin. The linkages connecting the spindles form a trapezoid, with the base of the
trapezoid formed by the rack and tie rods. The distance between the tie rod ends is less than
the distance between the kingpins. The wheels are parallel to each other when they are in the
straight-ahead position. However, when the wheels are turned, the inner wheel turns through a
greater angle than the outer wheel. Figure 7.2 also shows that the layout is governed by the
ratio of track (distance between the wheels) to wheelbase (distance between front and rear
wheels). The Ackerman layout is accurate only in three positions: straight ahead, and at one
position in each direction. The slight errors present in other positions are compensated for by
the deflection of the pneumatic tires.
For the purposes of this book, "steering mechanism" refers to those components required to
realize the Ackerman system. Of course, all vehicles today use a steering wheel as the interface
between the system and driver. (This has not always been the case. Early automobiles used a
tiller.) The steering wheel rotates a column, and this column is the input to the steering
mechanism.
These mechanisms can be broadly grouped into two categories:
(I) worm-type mechanisms, and
(2) rack and pinion mechanisms
1.WORM SYSTEMS (STEERING GEARS)

A.STEERING SYSTEMS AND STEERING DYNAMICS

Figure 7.3 shows the steering linkages required by worm gear steering systems. The Pitman arm
converts the rotational motion of the steering box output into side-to-side motion of the center
link. The center link is tied to the steering arms by the tie rods, and the side-to-side motion
causes the spindles to pivot around their respective steering axes (kingpins). To achieve
Ackerman steering, the four-bar linkages must form a trapezoid instead of a parallelogram
(refer to Fig. 7.2). Although all worm-type steering systems use linkages similar to these, the
specifics of the steering boxes differ
WHEEL ALIGNMENT

In addition to allowing the vehicle to be turned, the steering system must be set up to allow the
vehicle to track straight ahead without steering input from the driver. Thus, an important
design factor for the vehicle is the wheel alignment. Four parameters are set by the designer,
and these must be checked regularly to ensure they are within the original vehicle
specifications.
The four parameters discussed here are as follows:
Automotive Engineering Fundamentals
1. Camber
2. Steering axis inclination (SAI)
3. Toe
4. Caster
1 Camber
Camber is the angle of the tire wheel with respect to the vertical as viewed from the front of
the vehicle, as shown in Fig. 7.17. Camber angles usually are very small, on the order of 1 ";the
camber angles shown in Fig. 7.17 are exaggerated. Positive camber is defined as the top of the
wheel being tilted away from the vehicle, whereas negative camber tilts the top of the wheel
toward the vehicle. Most vehicles use a small amount of positive camber, for reasons that will
be discussed in the next section. However, some off-road vehicles and race cars have zero or
slightly negative camber.
2. STEERING AXIS INCLINATION (SAI)
Steering axis inclination (SAI) is the angle from the vertical defined by the centerline passing
through the upper and lower ball joints. Usually, the upper ball joint is closer to the vehicle
centerline than the lower, as shown in Fig. 7.18.

Figure 7.18 also shows the advantage of combining positive camber with an inclined steering
axis. If a vertical steering axis is combined with zero camber (left side of Fig. 7.1 8), any steering
input requires the wheel to scrub in an arc around the steering axis. In addition to increasing
driver effort, it causes increased tire wear. The combination of SAI and positive camber reduces
the scrub radius (right side of Fig. 7.18). This reduces driver effort under low-speed turning
conditions and minimizes tire wear. An additional benefit of this system is that the wheel arc is
no longer parallel to the ground. Any turning of the wheel away from straight ahead causes it to
arc toward the ground. Because the ground is not movable, this causes the front of the vehicle
to be raised. This is not the minimum potential energy position for the vehicle; thus, the weight
of the vehicle tends to turn the wheel back to the straight ahead position. This phenomenon is
very evident on most vehicles-merely turning the steering wheel to full lock while the vehicle is
standing still will make the front end of the vehicle rise visibly. Although the stationary the
weight of the vehicle may not be sufficient to rotate the wheels back to the straight-ahead
position, as soon as the vehicle begins to move, the wheels will return to the straight-ahead
position without driver input.
Caster angle also contributes to this self-aligning torque and will be discussed in Section
7.4.4. Note that the diagrams in the preceding figures have been simplified to facilitate
discussion. In practice, the wheel is dished so that the scrub radius is further reduced, as
illustrated in Fig. 7.19.

3 TOE
Toe is defined as the difference of the distance between the leading edge of the wheels and the
distance between the trailing edge of the wheels when viewed from above. Toe-in means the
front of the wheels are closer than the rear; toe-out implies the opposite. Figure 7.20 shows
both cases.

Cross-sectional view of a wheel and tire assembly

Adapted from Automotive Engineering (1 982).
For a rear-wheel-drive vehicle, the front wheels normally have a slight amount of toe-in. Figure
7.18 shows why this is true. When the vehicle begins to roll, rolling resistance produces a force
through the tire contact patch perpendicular to the rolling axis. Due to the existence of the
scrub radius, this force produces a torque around the steering axis that tends to cause the
wheels to toe-out. The slight toe-in allows for this, and when rolling, the wheels align along the
axis of the vehicle. Conversely, front-wheel-drive vehicles require slight toeout. In this case, the
tractive force of the front wheels produces a moment about the steering axis that tends to toe
the wheels inward. In this case, proper toe-out absorbs this motion and allows the wheels to
parallel the direction of motion of the vehicle.
4. CASTER
Caster is the angle of the steering axis from the vertical as viewed from the side and is shown in
Fig. 7.21. Positive caster is defined as the steering axis inclined toward the rear of the vehicle.
 Figure 7.2 1. Caster angle.

With positive caster, the tire contact patch is aft of the intersection of the steering axis and the
ground. This is a desirable feature for stability, as illustrated by Fig. 7.22. When the wheel is
turned, the cornering force acts perpendicular to the wheel axis and through the contact patch.
This creates a torque about the steering axis that acts to center the wheel. Obviously, negative
caster results in the opposite effect, and the wheel would tend to continue turning about the
steering axis. The most common example of positive caster is a shopping cart. The wheels are
free to turn around the steering axis, and when the cart is pushed straight ahead, the wheels
self-align to the straight-ahead position.