Group
28
igni
t
ion systems
De
sig
n
and
funct
io
n
Compensa
t
io
n fun
c
tions
Reason for different re-advance rat
es
'
Faste
r'
re-
advance
rates
are possible in
the
lower speed
ranges
since
ig
n
i
t
ion
then takes place when the piston
is
closer
t
o
TDC and
t
he
risk
of
knock
is,
consequently, lower
.
Fa
st
re-advance
is
more advantageous since it serves
t
o
i
n
crease
th
e
mean
value of
the
t
iming angle
.
(
As
a
l
ready
described, advancing
the
point
im
proves
t
he effi-
ciency of
fuel
utilization
.)
'
Slower
'
re
-
advan
ce
rat
es
are
chosen
at higher
speeds since igni
ti
on
then t
akes
place relat
iv
ely
early
as
th
e
piston
move
s
upwards
towards
Toe
(and
th
e
attendant
r
is
k
of knock
greate
r
).
I
ncreasing
th
e
rat
e o
f
re
-
advance
un
der
t
hese
condi
t
ions
wou
ld g
r
ea
tly
inc
rea
se
t
he
likelihood
of recurring
knock
.
EZ
-
K
sys
tem
s
employ more
o
r
less the same method of varying the
re
-
advance
r
ates
following
k
noc
k
-controlle
d
retardation.
35