Subaru 1600 Service Manual page 178

2) Component parts of ECC system
1) Oxygen (0,) sensor
0,
sensor is a kind of concentration
cell that generates electromotive force
according to the ratio of
0,
concentra-
tion in air to that in exhaust gases, and
has a characteristic that the electro-
motive force is changed drastically
with respect to the stoichiometric air-
fuel ratio. The force is larger on the
rich side (smaller air-fuel ratio) and
smaller on the lean side (larger air-fuel
ratio) of the mixture.
0,
sensor is installed on exhaust
manifold.
Fig_ 5-11
A5-679
Contact plate
c
/Louver
~/Zirconia tube
A10-180
Fig.5-12
O
2
sensor
2) Electronic control module (ECM)
According to the signal from 0, sensor,
ECM judges whether the exhaust gas
at the manifold is made from rich or
lean mixture against the stoichiometric,
and issues signals to duty solenoid
valves. The current air-fuel ratio is
judged to be rich mixture when the
EMISSION CONTROL SYSTEM
electromotive force of
0,
sensor is
higher than the specified level. As the
result, ECM issues signals to duty
solenoid valves to let much air into
carburetor.
On the other hand, the air-fuel ratio is
judged to be lean mixture when the
electromotive force is lower. ECM
issues signals to duty solenoid valves
to let a little air into carburetor so that
the air-fuel ratio will be changed to-
ward rich mixture. According to these
feedback operations, the air-fuel ratio
maintains at around the stoichiometric
value.
A 10-181
Fig,5-13 Electronic control module
tEeM)
3) Duty solenoid valve
On Hitachi carburetor, two duty
solenoid valves are installed on the
intake manifold, while on CoW carbu-
retor, one duty solenoid valve is
unified in the carburetor as shown in
the figure.
Duty solenoid valve has a construction
as shown in the illustration.
The light-weight valve (A) repeats
opening! closing at a short cycle accord-
ing to the signal output from ECM.
The average flow rate of air passing
through this valve to carburetor
changes depending upon the period of
time during which the valve is opened,
thereby the air-fuel ratio is varied.
The status that a voltage is applied to
solenoid, that is, the valve is lifted is
called "ON-duty", and duty ratio is
given by the follOWing equation.
D t
t · ON-duty time
x
lOOot
o
u y ra
10
= - .
It
Cycle
1 cycle
-
~
[ON duty
Open
I
tJ
r - r -
A10-t)93
Fig. 5-14
The ON-duty duration varies at a fixed
acceleration, with the Rich-Lean
mixture as measured by the O
2
sensor.
In steady-state operation [where the
vacuum switch (II) is on], the accelera-
tion rate beyond a certain engine
speed is changed in steps to obtain
greater acceleration at higher engine
rpm. This allows the valve to sensitive·
ly respond to the Rich-Lean mixture
as
measured by the O
2
sensor.
(Hitachi)
I Duty solenoid valve (main)
2 Duty solenoid valve (slow)
3 Connectors
(C-W)
I Feedback: solenoid valve
2 Connector
Fig. 5-15
Al0-141
A10-142