Toyota COMPUTER-CONTROLLED SYSTEM - Hot-Wire Type

4
3 . HOT-WIRE TYPE
ELECTRONIC CONTROL
SYSTEM - Air Flow Mete r
Instead of measuring intake air volume in the man-
ner of other air flow meters, a hot-wire type air
flow meter measures intake air mass directly .
The structure is both compact and lightweight . In
addition, there is only a low level of intake
resistance by the sensor
.
Having no mechanical functions it offers a
superior durability .
Thermisto r
F
~ REFERENC E
A hot-wire type air flow meter as shown below
is used on some models .
OPERATION AND FUNCTI O
N
Current flows to the hot-wire (heater) causing it
to be heated . When air flows through the wire,
the hot-wire is cooled corresponding to the intake
air mass
. By controlling the current flowing to the
hot-wire in order to keep the hot-wire temperature
constant, that current becomes proportional to in-
take air mass . Intake air mass can then be
measured by detecting that current . In case of
hot-wire type air flow meters, this current is con-
verted into a voltage that is then output to the
Engine ECU .
Hot-wire (heater)
*
*Constant temperatur e
Thermistor
Intake air mass --
-
(g/sec .)