Vibration Theory; Exhaust System - Suzuki XL7 2007 Service Manual

Vibration Theory and Terminology

Vibration Theory

The designs and engineering requirements of vehicles
have undergone drastic changes over the last several
years.
Vehicles are stiffer and provide more isolation from road
input than they did previously. The structures of today's
stiffer vehicles are less susceptible to many of the
vibrations which could be present in vehicles of earlier
designs, however, vibrations can still be detected in a
more modern vehicle if a transfer path is created
between a rotating component and the body of the
vehicle.
There are not as many points of isolation from the road
in many vehicles today. If a component produces a
strong enough vibration, it may overcome the existing
isolation and the component needs to be repaired or
replaced.
The presence/absence of unwanted noise and vibration
is linked to the customer's perception of the overall
quality of the vehicle.
Vibration is the repetitive motion of an object, back and
forth, or up and down. The following components cause
most vehicle vibrations:
• A rotating component
• The engine combustion process firing impulses
Rotating components will cause vibrations when
excessive imbalance or runout is present. During
vibration diagnosis, the amount of allowable imbalance
or runout should be considered a TOLERANCE and not
a SPECIFICATION. In other words, the less imbalance
or runout the better.
Rotating components will cause a vibration concern
when they not properly isolated from the passenger
compartment: Engine firing pulses can be detected as a
vibration if a motor mount is collapsed.
A vibrating component operates at a consistent rate (km/
h, mph, or RPM). Measure the rate of vibration in
question. When the rate/speed is determined, relate the
vibration to a component that operates at an equal rate/
speed in order to pinpoint the source. Vibrations also
tend to transmit through the body structure to other
components. Therefore, just because the seat vibrates
does not mean the source of vibration is in the seat.
Vibrations consist of the following three elements:
• The source - the cause of the vibration
• The transfer path - the path the vibration travels
through the vehicle
• The responder - the component where the vibration is
felt
In the preceding picture, the source is the unbalanced
tire. The transfer path is the route the vibrations travels
through the vehicle's suspension system into the
steering column. The responder is the steering wheel,
which the customer reports as vibrating. Eliminating any
one of these three elements will usually correct the
condition. Decide, from the gathered information, which
element makes the most sense to repair. Adding a brace
to the steering column may keep the steering wheel from
vibrating, but adding a brace is not a practical solution.
The most direct and effective repair would be to properly
balance the tire.
Vibration can also produce noise. As an example,
consider a vehicle that has an exhaust pipe grounded to
the frame. The source of the vibration is the engine firing
impulses traveling through the exhaust. The transfer
path is a grounded or bound-up exhaust hanger. The
responder is the frame. The floor panel vibrates, acting
as a large speaker, which produces noise. The best
repair would be to eliminate the transfer path. Aligning
the exhaust system and correcting the grounded
condition at the frame would eliminate the transfer path.
General Information: 0A-18