Buick LeSabre 1965 Service Manual page 857

1 1 - 1 2 4 ELECTRO-CRUISE
ACCESSORIES
v ^aiSPEED SETTING &
NGAGEMENT KNOB
Figure 11-171 — Electro-Cruise Controls - 45000, 46000 and 48000 Series
5. SAFETY PRECAUTIONS - For
obvious s a f e t y reasons, the
Electro-Cruise should not be used
in areas where conditions are not
adapted to maintain a constant
speed, such as in city-type traffic,
winding or h i l l y roads, bad
weather, etc. The Electro-Cruise
should not be engaged when the
car is being driven on snow, ice
or mud.
b. Operation
1. POWER UNIT - The power
unit is basically a pneumatic
chamber and porting valve con-
sisting of: an aluminum housing
and cover; a power diaphragm and
bead chain assembly; a diaphragm
return and speed control com-
pensating spring; and air orfice;
a vacuum orfice; a control valve;
a control valve return spring; a
control valve coil; an air filter;
and brake release line fitting.
See figure 11-173.
In operation, the power unit re-
ceives an electric signal from
the electronic control unit which,
according to the dictates of the
speed transducer, ports the
proper vacuum and air mixture
into the unit to maintain the
desired road speed. The signal
which is received by the power
unit during normal cruise oper-
ation, cycles the control valve
armature between the atmosphere
and vacuum ports allowing the
armature to dwell on the ports
for time intervals depending upon
the shape of a square wave elec-
trical output from the speed
transducer.
When the control valve coil is
energized, the "teeter -totter"
armature of the control valve is
pulled down against spring ten-
sion, closing the air port to at-
mosphere and opening the vacuum
port to the diaphragm chamber.
The vacuum admitted, then, tends
to increase tension on the bead
chain to open the throttle valve.
Similarly, when the control valve
coil is not energized, spring ten-
sion positions the "teeter-totter"
armature of the control valve to
close the vacuum port and open
the air port to the diaphragm
chamber. The air admitted, then,
tends to reduce tension on the
bead chain to close the throttle
valve.
Thus through continual cycling of
the control valve, a vacuum level
is produced in the diaphragm
chamber proportional to the de-
mands of the speed transducer and
the tension of the bead chain bal-
ances the force of the existing
throttle return spring to maintain
the required throttle angle. Max-
imum throttle angle allowed by
the power unit is approximately
35°; therefore, when the control
valve coil is continuously ener-
gized, car acceleration will be
held at this angle. In addition,
the maximum speed of 90 MPH
is determined by this maximum
throttle opening.
2. SPEEDOMETER AND SPEED
TRANSDUCER - The speed trans-
ducer is integral with the speed-
ometer and utilizes a cam, cam
f o l l o w e r , oscillating contact
spring and pickup arm to control
the electrical impulses reflected
from the electronic control unit
to the power unit. See figure
11-174. Position of the oscillating
contact pin, which determines the
set speed, is adjusted by rotating
the cam follower mounting ring
through a gear arrangement with
the speed setting shaft and knob
assembly. Rotating the cam fol-
lower mounting ring also moves
the speed setting pointer to indi-
cate the relative position of the
oscillating contact pin, and, there-
fore, indicate the actual set speed.