Volvo 819 E - Temperature Sensor

Group 28 Igni t ion systems
Design
and function - Compensation funct ions
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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 ti ming at t emperatures deviating from the normal operating range (i.e. outside approx.
8O"C to 1000C). The temperature sensor is normally mounted in the cylinder head and is co mpletely immersed in the
coolant.
Construction
Th e temperature sensor consis ts 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 ted engines,
the dev ice is equipped with two resistors , one of which is connected to the fuel syst em control unit to provide a fuel
enrichment signal when the engine is cold and th e o ther to the ignition system control unit . (Twin-resistor temper-
ature sensors are normally grounded to the cylinder block, 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 rises. Since the control unit cont i nuously supplies the sensor w i th a constant current, the variat ion in resist-
ance is reflected
by the voltage drop across the device. enabling the control unit to determine when the various tem-
perat ure-dependent timing adjustments must be made.
B efore cons idering the beneficial effects of tempera ture compensation on the tim ing, some effort should be made to
gain an understanding of th e effects of variations in t iming on the cylinder, exhaust gas and coolan t temperatures .
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