Throttle Switch; Lambda-Sond; Sensors - Volvo 240 1989 Service Manual

Design and function
Fuel system LH2. 4 - 240
Obt009 mount!", bol.-
tor
adjun ino Iwheh Mtting
Fuiliolid
switch
~
Throttle __
--~~-"i~r&2])IS
spindle
C.m disc
Idle
switch
(micro SWiTCh)
Heatin':..-.Jt...-H­
=
n.m
Sensor
The exhaust gases reach the outer surface of the
Lambda"sond sensor via slits in the protective
sleeve . Ambient air reaches the sensor's inner
surface via channels. The sensor itself consists of a
pfatinum covered zirconium-oxide pipe.
The Lambda-sond signal strength is in direcf propor­
tion to the amount of oxygen in the exhaust gases.
This depends on the airlfuel ratio. A Lambda value of
1 represents the theoretically perfect ratio. A rich
mixture results in a higher voltage and a lean mixture
gives the opposite result.
The current sent by the Lambda-sond to the control
unit varies between 0.1 and 1.0 volt .
The shift between high and low voltage occurs when
the Lambda value is at 1. The control unit uses this
information to adjust the amount of fuel injected.
o
Throttle switch
Tells the fuel system and ignition system control units
whether the throttle valve is closed or fully open.
o
Lambda-sond
Under normal conditions, the optimum mixture ratio
is 14.7kg air to 1kg fuel. The ratio is monitored by
post-combustion measurement of the oxygen con­
tent in the exhaust gas using the Lambda-sond.
This particular model of Lambda-sond is known as a
"comparing Lambda-sond'. It produces a measure­
able current by comparing the amount of oxygen in
the exhaust gas with the amount in the ambient air.
The Larnbda-sondoperates only within a certaintem­
perature range - approx . 285-850°C, (545-1530°F).
It is electrically heated to enable it to reach operat­
ing temperature quickly . When the ignition is turned
on, current is sent to a PTC resistor (Positive Tem­
perature Coefficient) whose resistance increases
with rising temperature. Because of this system, the
Lambda-sond quickly reaches correct operating
temperature, even at low exhaust gas temperatures.
The Lambda·sond is mounted in th e exhaust gas mani­
fold about 15 cm (6 in.)
in
front of the catalytic co nverter.
12