Bentley R Type - Automatic Choke Control

Tnr Furr
Sysrnu.
Automatic
Choke Gontrol.
The
automatic system
consists
of:-
(i) Al
out-of-balance
butterfly
rqln.
-in
the
common
air
intake
pipe, indirectly
coupled
to
a diaphragm
which
is
subject
to
induction
pipe
depression.
(ii) A small
electro-magnet
wired in parallel
in the
ignition
circuit,
which holds
the butterfly
closed
when
starting.
(iii) A cam
for
"fast
idle",
loose-coupled
to
a pick-up
lever
con-
nected to
the butterfly
valve
spindle.
(iv) A
thermostatic
spring
unit
housed in
a
suitable
recess in
the
water
jacketing
of the
induction
manifold.
As the
engine
cools, the
thermostatic
spring
also
cools,
and
gradually
gains
tension.
The thermostatic
spring
is, however,
unable
to close the choke
valve until
the
throttle
stop
screw has been
lifted
from
the
fast idle cam.
,
It i; theryfore
necessary
to depress
the accelerator
fedal
slightly
and
then
allow it
to return
to its normal
position
be.fore
attempting
to- make
a
start.
on
releasing
the accelerator
pedal,
the throttle
opening
is
greater
than that
{or
normal
idling, by
virtue of
the extra.
stop
resting
on
the
"fast
idle"
cam.
When
the ignition
is switched
on, the
electro
magnet
wired in
parallel is energised
and the
armature
on the
butterfly
spindle
holds
the choke valve
in the
closed position.
On starting
the engine,
the
valve
is
held closed
until the
oil pressure
builds
up to
a
pre-determined
value to operate
the oil pressure
switch and
so release
the
choke valve
to take up its normal
open position.
As soon as the
engine
is running,
the
depression
created in
the
induction
pipe
is
exerted
on the
diaphragm
which
transmits
its energy
to the loose lever
on the butterfly
spindle.
This
in turn
catches up
on a peg and
turns
the spindle
to open the
butterfly
valve a
pre-
determined
amount,
against
the loading
of the
thermostatic
spiing.
Assuming
that
the accelerator
pedal
has
not been
moved,
the
engine will
continue
to run at
a speed
determined
by
the
starting
position
of
the
"fast
idle"
cam.
The engine coolant
jacketed
pocket
holding
the thermostatic
coil units
will
gradually
warm up and
transnit heat
to the
coil.
This in turn
will wind
up
and
gradually
release
the load
on the butterfly,
which will
gradually
open.
With the
depression
of
the accelerator
pedal
for
the
drive
away,
the
"fast
idle"
stop on the
throttle shaft
will move
away
from
the cam
and the
cam will fall
on to the
pick-up
lever
coupled
to the butterfly
spindle.
The loading
of the thermostatic
spring and
the off-set
of
the butterfly
have been
so
arranged
that any
air flow
greater than
thlt
^required
for
a
"fast
idle"
automatically
opens the butterffy
sufficient
for
engine requirements,
5r