1
®
8V
1
2
3
4
5
6
7
MACK
CAT
DETROIT
DIESEL
0V
DESCRIPTION
The ET-2
™
is an electronic throttle. On electronically
controlled diesel engines, the ET-2
™
treadle fulfills the same
function as a conventional mechanical throttle. The ET-2
™
treadle controls engine speed by interacting with an
electronic fuel management controller on the engine, rather
than transmitting a mechanical force from the throttle pedal
to the engine governor.
The main components of the ET-2
™
throttle are a cast
aluminum mounting base and treadle, a rubber treadle cover,
a potentiometer (variable resistor), and a roller assembly.
The potentiometer is specific to each engine application.
OPERATION
The ET-2
™
treadle provides smooth, graduated throttle control
through the function of its variable resistor, or potentiometer.
The ET-2
™
treadle receives its supply voltage from the engine
control unit. The lever shaft connects the roller assembly
to the potentiometer, so that any movement of the treadle
rotates the potentiometer. As the potentiometer rotates,
its resistance changes. This way, the potentiometer
communicates the throttle position to the fuel control
system by changing resistance, returning more or less of
the supplied voltage back to the electronic engine controller.
If the driver does not request engine power, the throttle is in
the idle (or “closed throttle”) position. In this state, the
potentiometer significantly reduces the amount of supply
voltage returned to the engine control unit (See Figure 2).
As the driver depresses the ET-2
™
treadle, output voltage
increases (see Figure 3). The potentiometer allows an
increased amount of its supply voltage to return to the engine
control unit, which in turn increases the engine’s speed.
In the full (or “open throttle”) position, the driver has fully
depressed the ET-2
™
treadle. This is the state of least
potentiometer resistance. The ET-2
™
treadle returns the
maximum percentage of supply voltage to the engine control
unit (see Figure 2).
SD-15-4106
Engine
Idle Throttle
Full Throttle
Manufacturer
(Closed)
(Open)
CAT
13 - 21%
79 - 89%
Cummins
8 - 18%
70 - 80%
Detroit Diesel
6 - 14%
86 - 94%
Mack
10 - 20%
70 - 85%
FIGURE 2 - ET-2
™
TREADLE OUTPUT VOLTAGE, AS A
PERCENTAGE OF SUPPLY VOLTAGE
FIGURE 3 - ET-2
™
TREADLE OUTPUT VOLTAGE
CLOSED THROTTLE
OPEN THROTTLE
ET-2
™
TREADLE
OUTPUT
VOLTAGE
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OR
CUMMINS
Bendix
®
ET-2
™
Electronic Treadle
CONNECTOR
FIGURE 1 - ET-2
™
ELECTRONIC TREADLE
TREADLE
COVER
CABLE ASSEMBLY
ROLLER
MOUNTING BASE
DOUBLE RETURN
SPRING
PIVOT SPRING
POTENTIOMETER
