Triumph TR7 - Page 14

EMISSION AND EVAPORATIVE LOSS CONTROL SYSTEMS
To measure the air flow Into the engine an Air Flow Meter is
fitted
In the engine compartment between the air cleaner and
a
plenum chamber above the engine. The plenum chamber
acts
as a collecting bOil: for the mgolng air and helps to
smooth out any rapId fluctuations in air flow that might upset
the Air Flow Meter signals.
The AIr Flow Meter Iiself IS basically a short tube In which
there is a pivoted measUring flap that IS moved by air flowing
past It Into the engine To reduce excessive fluttering of this
flap, such as would be caused by sudden changes or pulses
in the air flow. a compensating flap IS fllted as part of the
same
casting as the measuring Ilap_ The position of the
measunng flap IS controlled by the alf drawn into the engme
and the action of a coil return spring The mass of air drawn
Into the engine at any time IS Indlcatrve of the engine load
and a SIgnal. proportional
to the flap position. is passed to
the
EC.U
However. the air mass IS related to air denSItY which In turn IS
dependant upon aIr temperature Therefore an AIr
Temperature Sensor IS Incorporated Into the Air Flow Meter
and this sends a separate electrical Signal to the EC U
Due to the action of the COil return spring. the Air Flow Meter
measuring flap IS almost closed when the engine IS Idling
and an Idle aIr by-pass channel IS provIded to assIst the
engine to breathe at this low speed Air passing through the
by-pass channel
IS not registered by the Air Flow Meter
measuring flap
"."
Fig.14 Air flow m.t ....
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