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48
3.
ENGINE
X
X
Fig. 3. 99
0%
Balance
Fig. 3. 100
30%
Balance
X
FR/
X
I
I
Fig
.
3
.
101
100
%
Balance
~
L-
-
----
--1
l---a~-+
---
--
-~~~~~
Reciprocating
mass-
.!
m'
- L
Rotating
mass=~ m'
m=
The who
le
connecting
rod
mass
G = The
centroid position
y
Fig. 3. 102
Cannecfing
rod
ratoting moss
and
reciprocating
mass
M
:
Reciprocating
moss
(piston,
piston pin and
connecting rod)
The
X-X
and
Y-Y
axes
are
shown in
Fig. 3. 98.
First,
consider the
case
in which
the
crankshaft
is
perfectly balanced (m
=
OJ.
The
cycle of
inertial
force applied to
the
shaft
"0"
due to
the
recipro-
cating mass M
in
the
X-X
direction
develops
into
engine
vibrat ion.
This
is called 0%
balance
.
Next,
if
a
we
ight
equal to 30% of M (counter-
weig ht)
is atroched
to the
opposite side
of
the
crankpin,
the
size of the inertial
force in
the
direction
of
X-X
is reduced to
0.
7
X
M.
However,
the
crankshaft becomes unbalanced (m-0 .31
and develops
a centrifugal
force which will
produce a
vibration
in the
Y-Y
direction.
This
is
called
30%
balance.
(Fig. 3. 100)
In other words,
the
vibration in
the
X-X
direction has diminished but
increased in
the
Y-Y
direct ion by the
like amoumt.
This total
hos
been expressed
in
percentage.
If the counterweight
is made
equal
to
M, the
tota
l
vibration in
the
X-X
direction
will
be trans-
ferred
to
the Y-Y direction.
This
is
called 100%
balance.
(Fig. 3. 101)
G
.
Connecting Rod Construction
The
connecting rod (commonly
ca ll conrod
l
is a
link connecting
the
piston and
the
crank
pin.
The
small end which
is connecting
to the
piston performs
reciprocating motion while the
large end connected
to the
crank
pin
performs
the
rotary
motion.
The
connecting
rod, therefore, receives a combination
of
different
forces.
The connecting rod mass is divi-
ded
into
the rotating mass and the reciprocating
moss
in
the
ratio
to
the
distance
from
the
connecting rod
centroid.
The
center
of
the con-
nect
ing
rod
masses is
assumed by having
the
rotating
moss
concentrate
at
the large end and
the
rec iprocating
mass
at
the
small end.
(Fig.
3. 102)
The
connecting rod
is an H
shaped
forging
made of
chrome
moly
bdenum steel
with
needle
roller
bearings
install
in
the large
end.
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