ENGINE GOVERNING ..... Troubleshooting

ENGINE GOVERNING ..... Troubleshooting
ENGINE
GOVERNING
.....
Troubleshooting
SYSTEMS
TROUBLE
section
SHOOTING
If the governor does not operate, measuring, in sequence,
voltage between the various speed control unit terminals and
ground (Terminals F, G, H and T are ground) will indicate
TERMINALS
S
EG 100-2
the possible fault. Should all 5 voltage tests indicate normal
values, the defect must be in'the actuator or in the wiring to
the actuator. (See Section on Defective Actuators on page 2).
/
NORMAL VALUE
1.0 VAC - RMS minimum
while cranking.
PROBABLE CAUSE OF NON-NORMAL
READING
1. Defective magnetic speed sensor.
2. Gap too large between speed sensor and gear teeth.
3. Improper or defective wiring to the speed sensor.
Kmmmm
1. DC power not connected or low battery voltage.
(Internal regulated DC supply)
2. Speed trim control shorted, ground or miswired.
3. Wiring error.
4. Defective speed control unit.
L
Above 5.1 VDC while cranking.
(Inverse speed error signal.)
1. Frequency adjust set too low. Turn CW.
2. Defective speed control unit.
Above 5.1 volts is under speed
signal. Below 5.1 volts is over speed
signal.
On speed will indicate a steady 5.1
volts.
N
8.5 to 9.5 VDC while cranking.
(Proportional actuator voltage.)
'1. Defective speed control unit.
2. Battery voltage may be too low while cranking.
B
2.5 VDC maximum while cranking.
(Transistor voltage.)
1. Output transistor open (defective speed control unit).
2. Defective actuator (see page 2).
3. Error in wiring to actuator.
OTHER TROUBLE
SYMPTOM
SHOOTING
TEST
TESTS
PROBABLE
TROUBLE
Engine overspeeds
Determine voltage on terminal "L".
Should be less than 5.1 VDC.
1. Frequency set too high. Turn frequency
adjust CCW.
2. Defective speed control unit.
Engine overspeeds
Measure the voltage across the insulated nut
located on the side of the control unit.
Should be more than 2.5 VDC.
1. Output transistor shorted.
(Defective speed control unit.)
2. Wiring to actuator incorrect.
Fhrottle does not move
Measure battery voltage at the battery while
cranking. Must be 8.0 VDC minimum,
1. Insufficient battery voltage. Put a
momentary connection from terminal "B"
on the control unit to negative ground
while cranking (Terminal "G" is ground).
2. Replace with battery of higher amp hour
rating.
l'hrottle does not move
Ground the insulated nut located on the side
of the speed control unit, except on CU
673C-10 speed control units. Throttle should
move to full open position.
1. Wiring to actuator or battery incorrect.
2. Actuator or linkage bound.
3. Defective actuator. (See page 2.)
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in U S A
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1984
Page 1
ENGINE
GOVERNING
Troubleshooting
SYSTEMS
ERRATIC
A. INSUFFICIENT
MAGNETIC
OR UNSTABLE
PICKUP SIGNAL
Although the speed control unit will govern well on. 0.5
volts RMS signal if it is a clean sine wave, a signal from
the magnetic speed sensor of 3 volts RMS at full speed
will eliminate any possibility of missed or extra pulses.
This signal is mesured at terminals "S" and "T".
B. ELECTRICAL
NOISE
OR UNWANTED
DROOP
If noisy electrical devices are present, such as magnetos,
solid state ignition systems battery chargers or regulators
which emit radio frequency interference (RFI), then
unstable governing or droop may be noticed. The speed
control unit has internal filters which provide some protection from radio frequency interference. Excessive
levels of RFI must be treated separately. A metal shield
placed around the emitting source will help. Placing the
governor harness and speed control unit as far away as
possible from the emitting source will hdp. Always twist
the leads from the magnetic speed sensor all the way
back to the speed control unit. Shield the speed sensor
leads with the shielding connected to terminal "T" of
the speed control unit only. Raise the magnetic speed
sensor voltage by reducing the gap between the speed
sensor and the ring gear. A gap of 0.030" will provide a
strong signal. If noise is still present, a capacitor (1,000
mfd, 12 - 20 volts) may be connected across the speed
trim control, terminal K + to terminal F -. This will
reduce external interference coming from the power supply. When extreme RFI is encountered, it may be
necessary to shield all the leads to the speed control unit.
The shield should be grounded at terminal "G" of the
speed control unit.
C. DEFECTIVE
ACTUATOR
Should the coils of the actuator become open or shorted,
replace the actuator. If the coils are not open or shorted,
the wiring or connectors are defective,
D. LOW SPEED SURGING
OR PERIODIC
INSTABILITY
Each engine has certain response characteristics to which
the governor must be adjusted to match. The increase or
decrease of speed, as load on the engine changes, can be
reduced to a minimum by proper adjustment of the gain
control. Turning the gain control CW will shorten the
amount of speed change. Too much gain adjustment will
result in rapid throttle movement, which is instability,
The amount of time which the engine needs to completely regain the set speed, after a load change, can be reduced to a minimum by turning the stability control CW.
Excess CW adjustment will cause instability, usually in
the form of a low frequency
_JIi_lhItO
surge,
section
EG 100-2
GOVERNING
The governor system can be properly adjusted by the
following procedure. Under no load conditions, turn the
gain control CW until instability*occurs. Then back off
(CCW) until stability is restored. Next, turn the stability
control CW untit instability occut'e. Then back off
(CCW) until stability is restored. Once more, adjust the
gain control as above. Apply various loads up to full
loacl to insure that stability is fLxed at all loads. If not,
reset the gain and stability adjustments,
as above, under
whatever load condition indicates some instability.
If the gain control is nearly full CCW or the engine is
unstable at any' position of the gain and stability control,
proceed as follows:
Note the frequency of instability. In the instance of slow
speed surging of about 1-3 oscillations per second, modifying the speed control for added dead time compensation (derivitive) will improve performance and stabilize
the system. Connect a jumper from terminals "M" to
"H" (if serial number is less than 2R 6239, an external
capacitor is requied-see Service Letter EG-3 for details).
Readjust the gain and stability as mentioned above.
Some improvement must be noticed or the cause of instability lies elsewhere.
-I,.._/'J
If the frequency of instability is very fast, such as 8-10
oscillations per second, then the dead time compensation
can be reduced. Jumper "M" to "N". Readjust the gain
and stability as above.
If the governor system allows for stable operation but
speed overshoot is experienced because the gain control is
almost fully CCW, a modification
can be made to extend
the gain control setting. Apply a 6.8K ohm resistor from
terminal "L" to terminal "P". This will center the gain
adjustment and improve its stability.
Another cause of instability is in the linkage arrangement. Any binding or high friction loads can cause instability. Use unibaU joints on each end of the linkage
rod. A maximum of 10 degrees misalignment of the
linkage
rod be
canin be
tolerated.
movement must
excess
of 8 ° The
and useful
less thanactuator
12 °. Calculate
the ratio of throttle motion to actuator motion and
design the rod length and position on the throttle arm
and actuator arm accordingly. The rod length should be
such that the actuator is slightly off the stop when the
throttle lever is in full shutoff position. Similarly, the rod
length should be such that the actuator is slightly off the
full travel stop when the throttle lever is in full fuel position. Before starting, make sure the linkage is free of any
obstruction or binding. Manually push the actuator arm
to full fuel position and release it. It must spring instantly to the shutoff position.
ill UISA
Is_qtl(!O
Page 2
I)_Cpll_l,'I
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198.1
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