770G and 772G Off-Highway Truck (OEM) Hydraulic and Braking System: Hoist Control, Position Sensor (Hoist Control) & Limit Switch (Truck Body Up)

1.-Hoist Control

(1) RAISE position (2) HOLD position (3) FLOAT position(4) LOWER position

The hoist control is located to the right of the operator. The hoist control has four positions: RAISE, HOLD, FLOAT and LOWER. The machine should normally be operated with the hoist control in the FLOAT position.

The hoist control is connected to the hoist control position sensor which is a pulse width modulated sensor. The hoist control position sensor sends signals to the chassis ECM. The position of the hoist control will energize the appropriate solenoid on the hoist valve. See the hydraulic system System Operation, "Position Sensor (Hoist Control)" for additional information.

When the hoist control is released a spring will move the hoist control from the RAISE position to the HOLD position or from the LOWER position to the FLOAT position.

2.-Position Sensor (Hoist Control)

Location of the hoist control position sensor (1) Hoist control(2) Position sensor for the hoist control

Position sensor (2) is located on the right side of the operator's seat, and attached to hoist control (1). Position sensor (2) is a Pulse Width Modulation position sensor. Position sensor (2) sends duty cycle signals to the Chassis Electronic Control Module (Chassis ECM).

Note: Position sensor (2) does not need to be manually calibrated or adjusted. The machine performs an auto-calibration on the hoist control position sensor.

When the hoist control (1) is used, the position sensor (2) sends an electrical signal to the Chassis Electronic Control Module (Chassis ECM). The Chassis ECM uses this signal to energize the appropriate hoist proportioning solenoid on the hoist control valve. These hoist proportioning solenoids allow the spool in the hoist control valve to move. This will cause oil to be sent to the hoist cylinders in order to move the dump body.

The signal from the position sensor (2) is also used to neutralize the transmission. The Chassis ECM will allow only a forward speed position or the NEUTRAL position when position sensor (2) is in the RAISE position. The Chassis ECM will not allow a shift to the REVERSE position until the position sensor (2) has been moved from the RAISE position and the transmission shift lever is in the NEUTRAL position.

Note: If the machine is in REVERSE and position sensor (2) is in the RAISE position the Chassis ECM will shift the transmission to NEUTRAL. The machine will remain in NEUTRAL until hoist control (1) is moved into the HOLD or the FLOAT position and the transmission control has been cycled through NEUTRAL.

3.-Limit Switch (Truck Body Up)

(1) Truck body position plate (2) Limit Switch (Truck Body Up)(3) Lever

Truck body up limit switch (2) is located on a bracket on the rear, left side of the frame. Truck body position plate (1) is welded to the truck body. When the truck body is raised, truck body position plate (1) allows lever (3) to rotate upward in a counterclockwise direction. As lever (3) moves upward, truck body up limit switch (2) sends a signal to the Chassis Electronic Control Module (ECM). The signal indicates that the truck body is in the UP position.

When the truck body is lowered, truck body position plate (1) pushes lever (3) downward in a clockwise direction. As lever (3) moves downward, truck body up limit switch (2) sends a signal to the Chassis (ECM). This signal indicates that the truck body is DOWN. The adjustment of truck body up limit switch (2) is important. Refer to the Hydraulic System Testing and Adjusting, "Limit Switch (Truck Body Up) - Adjust" for the proper adjustment procedure.

Truck body up limit switch (2) will limit the top gear that is being used while the truck body is in the UP position. The Chassis (ECM) comes from the factory with the top gear value that is set to FIRST gear. The transmission will not shift past FIRST gear until the truck body is down. The top gear value is programmable by utilizing the Electronic Technician (ET). The top gear value can be changed to SECOND gear, or THIRD gear.

The signal from truck body up limit switch (2) is also used to control the SNUB position of the hoist control valve. The Chassis (ECM) signals the hoist proportioning solenoids. The solenoids move the hoist control valve to the SNUB position when the truck body is lowered or nears the frame. The speed in FLOAT is reduced in the SNUB position in order to prevent the truck body from contacting the frame too hard.

The signal from truck body up limit switch (2) is used to provide warnings to the operator. The signal warns the operator when the truck is moving with the truck body in the UP position.

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770G and 772G Off-Highway Truck (OEM) Hydraulic and Braking System: Hoist Control, Position Sensor (Hoist Control) & Limit Switch (Truck Body Up) 2013-01-04T14:28:00-08:00 Rating: 4.5 Diposkan Oleh: Unknown