Group
2
8
Igni
t
ion s
y
ste
m
s
Design and function
Compensation
funct
ions
[]
3
Temperature sensor
Function
and
location
The
control
unit
(1) compensates
the tim
ing
for engine temperature with the aid
of
the temperature
sensor (2).
This
function is used to adjust the t
i
ming at
t
emperatures
deviating from the normal
operating
range
(i.e.
outside approx.
t
o
The
temperature sensor is normally mounted in the
cylinder
head and
is
co
mpletely
immersed in
the
coolant.
Construction
Th
e
temperature
sensor
consis
t
s of
a
connector (3)
and a body
(
4
)
provided with a male
thread
and enclosing one or
two temperature
-sensitive
resistors
(5)
w
ith a
negative
temperatur
e coefficient (NTC). On
most
fuel
-
injec
t
e
d
engines,
the
dev
ice
is equipped with two resistors
,
one of
which
is connected
to the
fuel
sys
t
em control
unit
t
o
provide a fuel
enrichment signal when the engine
cold
and
th
e o
ther
to
th
e ignition system control
unit
.
(Twin-resistor temper-
ature
are normally
grounded
to the
cylinder
while the
single-resistor
type
is
grounded
through the
control unit
.)
Signal
The resistance of the temperature
sensor varies
in
direct pr
o
pon
ion
to the
coolant
temperature
.
falling as the
tem
-
perature
Since
the
control
unit cont
i
nuously
supplies
the
sensor
w
i
th
a
constant current,
the
va
riat
ion in
resist-
ance
is
reflected by the
voltage
drop across the device. enabling the
control
unit
t
o
determine when the various tem-
pera
t
ure-dependent timing adjustments must
be
made.
B
efore
cons
idering the
beneficial effects
of
tempera
t
ure compensation on
t
he
tim
ing, some
effort should be
made
t
o
gain
an
understanding
of
th
e effects of variations in
t
iming on the
cy
l
inder, exhaust gas and coolan
t
temperatures
.
4
1
