Group
28
Igni
t
io
n
systems
D
esign and
funct
ion
Compensation functions
Throttle switchlidling (air control) switch
Function and location
The
throttle
swi
tch
(1)
sup
plie
s
a
signal
to
the ignition system
c
ontrol
unit
when the throttle
is
fully
closed.
The
si
gnal
is
u
sed
t
o enable
th
e con
t
rol unit
(
4)
to
selec
t
a
t
im
ing
setting
whi
ch
is
sui
t
able
for
idli
ng
and
engi
n
e
braking
con
d
i
-
ti
ons. The
thr
o
tt
le swi
t
ch
detects the
throttle position
(
2)
by
measuring
the
rotation of
t
he spindle (3).
Signal
Thr
o
tt
le
closure
(for example under idling and engine braking
condi
tion
sJ
grounds one
o
f
the
s
w
i
t
ch
terminals
,
al-
lowing
a
cu
rrent to
flow from
one o
f th
e
term
i
nals on the
con
tr
ol uni
t
.
The ground current
is
interpreted
by
t
he con-
trol
unit
to
determine
,
on
the
bas
i
s of engine
spee
d
info
rmat
ion,
whether the conditions are
those
of idling or engine
brak
ing.
Idling
At
speeds
close
to idling
,
the
signal causes
the
control
un
i
t to adopt a
'
f
i
xed
'
igni
t
ion
setting
in
with the
idling program
.
Since
the
engine
is
not required to develop a
specific
power when idling
,
t
he
timing
is
determined
ma
i
nly
on
the
basis of max
i
mum
comfort.
Th
is
means
t
hat the
se
tt
i
ng
is
well
re
tarded
(
between
approx
.
10"
and
before ToC
)
to
minimize
the
peak
(i.e.
maximum)
pressure
in the
c
ombustion chamber
during the
combus
t
ion
phase
,
ensuring
smoo
t
h
,
s
t
eady
running.
Engine braking
Since
th
e s
p
eed
is
h
igher
under
e
n
gine
braking
co
nditions,
t
he control unit
timing
cha
ra
c
t
eris
t
ic is spee
d
-
dependent
only.
In
general
,
t
he cha
ra
c
teri
s
t
ic
represent
s
an o
p
t
imum compromise
between
th
e lo
we
s
t p
ossi
bl
e
emissions
and
mi
ni
mum
fuel
cons
umpt
io
n
.
(
M
os
t
of
t
he
elec
t
ronic fuel
i
njection
s
y
s
t
ems used
fea
t
ur
e a
fuel
cu
t
-o
ff
f
u
n
c
ti
on
which intervenes
und
er eng
ine b
r
ak-
i
ng
con
d
i
ti
ons.
In
t
his case,
the fuel
system control
unit
is also
su
pplied with a fUlly-closed
thr
o
ttl
e signa
l
and
keeps
the
i
n
jec
t
ors
f
ully closed under
these
condi
t
ions.)
Throttle switch type
s
A
.
Pr
ac
t
ically all
fue
l·injec
t
ed models
i
n
the
700 series are
f
i
ned
with
the
type of
throttle
switch
i
llustrated
.
The
s
w
i
t
ch
is
mounted on
the thrott
le
spindle
(3J,
which actua
t
es
cam plate
(5)
and an arm
(6).
The
arm opera
tes
a
microswitch
(7)
which
closes
to
g
r
ound
a terminal
in
the
connec
tor
(
8)
.
(
Apart from
supplying a signal
to the
control
unit
when the throttle
is closed,
the
type of switch used on some
en-
gine variants
i
ncorporates a
se
t
of
full·load
contacts (9)
wh
ich close
when
the
t
hrottle
is
fully
In
th
is
case,
a
full
-loa
d
signal
is fed
to
the fuel
system control
unit
,
ins
tru
c
t
ing i
t
to extend
the
injector opening period.
However
,
this feature
is
not used on
turb
ocharged engines.)
C
.
The
E
Z-118K
sys
tem
employs an
idling s
witch
(12) mounted
on
th
e
throttle
ca
ble pulley to
indicate
w
hen
the
thr
ottle
is
fully closed
.
The
con
tr
ol
units use
t
he
signal
t
o
establish a
com
fortable t
iming
setting
when
idling
and
to
activate
th
e
fue
l
cu
t
-off
functi
on
under
engine braking
con
dit
ions.
The
EZ
-
118
K control uni
t
also
uses
the
s
i
gnal
as
a
condi
t
ion
for
advancing the
tim
ing
for
i
dl
ing
speed
compensa
ti
on when
dr
ive
posit
io
n
is
se
l
ec
ted
on
an
au
t
omatic
mode
l
or
th
e
AC
compressor is switched in.
It
is ex
tr
emely
imponant
that
t
he
thr
o
ttl
e swi
t
Ch
be
co
r
rec
tly
adjusted before
chec
k
ing
the
timing, t
o
ensure
that
the
idling
setting
is correctly measured.
El
ectron
ic
ign
it
ion systems no
t
equi
pp
ed
with
a
throttle
s
witch
or
idling
(air
con
trol)
s
w
itch a
r
e supplied
w
i
th
i
nf
o
rmation
on
i
d
ling conditions
in
the
form of a
sig
nal
representing the vacuum in the intake manifold.
40
