®
Bendix® ET-2™Electronic Treadle
TREADLE
COVER
POTENTIOMETER
DOUBLE RETURN
SPRING
PIVOT SPRING
ROLLER
MOUNTING BASE
CABLE ASSEMBLY
CONNECTOR
FIGURE 1 - ET-2™ELECTRONIC TREADLE
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
SD-15-4106
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).
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
| 8V | | | CAT |
| 7 | | |
| | | |
ET-2™ | 6 | | | |
5 | | | |
TREADLE | | | |
OUTPUT | | | | |
VOLTAGE | 4 | | | MACK |
| | | |
| 3 | | | |
| 2 | | | |
| 1 | DETROIT | OR | CUMMINS |
| | DIESEL | | |
| 0V | | | |
| CLOSED THROTTLE | | OPEN THROTTLE |
FIGURE 3 - ET-2™ | TREADLE OUTPUT VOLTAGE |
